Fix triangle count validation in WriteSTLBinary function

[chrisreddington]

Correct the validation logic for the triangle count to ensure it does not allow negative values.

[github-actions]

Code Coverage Report

github.com/github/gh-skyline/ascii/generator.go:19:		GenerateASCII			87.1%
github.com/github/gh-skyline/ascii/generator.go:87:		sortContributionDays		85.0%
github.com/github/gh-skyline/ascii/generator.go:127:		getBlockType			100.0%
github.com/github/gh-skyline/ascii/generator.go:146:		getBlock			100.0%
github.com/github/gh-skyline/ascii/text.go:31:			centerText			100.0%
github.com/github/gh-skyline/errors/errors.go:28:		Error				100.0%
github.com/github/gh-skyline/errors/errors.go:36:		New				100.0%
github.com/github/gh-skyline/errors/errors.go:46:		Wrap				100.0%
github.com/github/gh-skyline/errors/errors.go:69:		Is				100.0%
github.com/github/gh-skyline/errors/errors.go:78:		Unwrap				100.0%
github.com/github/gh-skyline/github/client.go:28:		NewClient			100.0%
github.com/github/gh-skyline/github/client.go:33:		GetAuthenticatedUser		100.0%
github.com/github/gh-skyline/github/client.go:48:		FetchContributions		94.4%
github.com/github/gh-skyline/github/client.go:111:		GetUserJoinYear			93.3%
github.com/github/gh-skyline/logger/logger.go:23:		String				100.0%
github.com/github/gh-skyline/logger/logger.go:44:		GetLogger			100.0%
github.com/github/gh-skyline/logger/logger.go:59:		SetLevel			100.0%
github.com/github/gh-skyline/logger/logger.go:66:		logf				91.7%
github.com/github/gh-skyline/logger/logger.go:90:		Debug				100.0%
github.com/github/gh-skyline/logger/logger.go:95:		Info				100.0%
github.com/github/gh-skyline/logger/logger.go:100:		Warning				0.0%
github.com/github/gh-skyline/logger/logger.go:105:		Error				100.0%
github.com/github/gh-skyline/main.go:30:			formatYearRange			100.0%
github.com/github/gh-skyline/main.go:38:			generateOutputFilename		100.0%
github.com/github/gh-skyline/main.go:44:			generateSkyline			72.5%
github.com/github/gh-skyline/main.go:121:			defaultGitHubClient		0.0%
github.com/github/gh-skyline/main.go:130:			fetchContributionData		87.5%
github.com/github/gh-skyline/main.go:147:			main				0.0%
github.com/github/gh-skyline/main.go:181:			parseYearRange			86.7%
github.com/github/gh-skyline/main.go:205:			validateYearRange		100.0%
github.com/github/gh-skyline/stl/generator.go:15:		GenerateSTL			100.0%
github.com/github/gh-skyline/stl/generator.go:29:		GenerateSTLRange		66.7%
github.com/github/gh-skyline/stl/generator.go:77:		validateInput			88.9%
github.com/github/gh-skyline/stl/generator.go:93:		calculateDimensions		90.9%
github.com/github/gh-skyline/stl/generator.go:122:		findMaxContributions		100.0%
github.com/github/gh-skyline/stl/generator.go:135:		findMaxContributionsAcrossYears	100.0%
github.com/github/gh-skyline/stl/generator.go:155:		generateModelGeometry		94.7%
github.com/github/gh-skyline/stl/generator.go:196:		generateBase			44.4%
github.com/github/gh-skyline/stl/generator.go:213:		generateText			58.3%
github.com/github/gh-skyline/stl/generator.go:236:		generateLogo			44.4%
github.com/github/gh-skyline/stl/generator.go:251:		estimateTriangleCount		100.0%
github.com/github/gh-skyline/stl/generator.go:268:		generateColumnsForYearRange	72.7%
github.com/github/gh-skyline/stl/generator.go:289:		CreateContributionGeometry	80.0%
github.com/github/gh-skyline/stl/geometry/assets.go:16:		writeTempFont			62.5%
github.com/github/gh-skyline/stl/geometry/assets.go:47:		getEmbeddedImage		56.2%
github.com/github/gh-skyline/stl/geometry/geometry.go:46:	NormalizeContribution		100.0%
github.com/github/gh-skyline/stl/geometry/geometry.go:66:	CreateContributionGeometry	92.3%
github.com/github/gh-skyline/stl/geometry/geometry.go:92:	CalculateMultiYearDimensions	100.0%
github.com/github/gh-skyline/stl/geometry/shapes.go:11:		CreateQuad			100.0%
github.com/github/gh-skyline/stl/geometry/shapes.go:24:		CreateCuboidBase		100.0%
github.com/github/gh-skyline/stl/geometry/shapes.go:31:		CreateColumn			100.0%
github.com/github/gh-skyline/stl/geometry/shapes.go:44:		CreateCube			100.0%
github.com/github/gh-skyline/stl/geometry/shapes.go:61:		createBox			100.0%
github.com/github/gh-skyline/stl/geometry/text.go:65:		Create3DText			0.0%
github.com/github/gh-skyline/stl/geometry/text.go:112:		renderText			0.0%
github.com/github/gh-skyline/stl/geometry/text.go:165:		GenerateImageGeometry		83.3%
github.com/github/gh-skyline/stl/geometry/text.go:190:		renderImage			84.6%
github.com/github/gh-skyline/stl/geometry/text.go:245:		isPixelActive			100.0%
github.com/github/gh-skyline/stl/geometry/vector.go:12:		validateVector			100.0%
github.com/github/gh-skyline/stl/geometry/vector.go:22:		calculateNormal			88.9%
github.com/github/gh-skyline/stl/geometry/vector.go:43:		isZeroVector			100.0%
github.com/github/gh-skyline/stl/geometry/vector.go:50:		vectorSubtract			100.0%
github.com/github/gh-skyline/stl/geometry/vector.go:60:		vectorCross			100.0%
github.com/github/gh-skyline/stl/geometry/vector.go:70:		normalizeVector			75.0%
github.com/github/gh-skyline/stl/stl.go:50:			writeFloat32			100.0%
github.com/github/gh-skyline/stl/stl.go:56:			writePoint3D			100.0%
github.com/github/gh-skyline/stl/stl.go:64:			writeSTLHeader			80.0%
github.com/github/gh-skyline/stl/stl.go:75:			writeTriangleCount		66.7%
github.com/github/gh-skyline/stl/stl.go:84:			writeTrianglesData		72.7%
github.com/github/gh-skyline/stl/stl.go:117:			WriteSTLBinary			68.2%
github.com/github/gh-skyline/stl/stl.go:159:			writeTriangleToBuffer		88.9%
github.com/github/gh-skyline/types/types.go:19:			IsAfter				100.0%
github.com/github/gh-skyline/types/types.go:30:			Validate			100.0%
github.com/github/gh-skyline/types/types.go:65:			IsValid				100.0%
github.com/github/gh-skyline/types/types.go:82:			ToFloat32			100.0%
github.com/github/gh-skyline/types/types.go:99:			Validate			100.0%
github.com/github/gh-skyline/types/types.go:125:		ToFloat32			100.0%
total:								(statements)			76.5%