Fix parseInt overflow check false negative

[carsonip]

Description: The current parseInt overflow check may return false negative for input like 27670116110564327410. This patch fixes the overflow checking.

Benchmark before change:

goos: darwin
goarch: amd64
pkg: benchmarks
BenchmarkJsonParserLarge
BenchmarkJsonParserLarge-12                               124323             46955 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserMedium
BenchmarkJsonParserMedium-12                              771728              7705 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserDeleteMedium
BenchmarkJsonParserDeleteMedium-12                        728377              8323 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualMedium
BenchmarkJsonParserEachKeyManualMedium-12                1000000              5590 ns/op             112 B/op          2 allocs/op
BenchmarkJsonParserEachKeyStructMedium
BenchmarkJsonParserEachKeyStructMedium-12                 965860              6122 ns/op             560 B/op         12 allocs/op
BenchmarkJsonParserObjectEachStructMedium
BenchmarkJsonParserObjectEachStructMedium-12              770988              7783 ns/op             512 B/op         11 allocs/op
BenchmarkJsonParserSmall
BenchmarkJsonParserSmall-12                              8176395               733 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualSmall
BenchmarkJsonParserEachKeyManualSmall-12                 9562789               629 ns/op              80 B/op          2 allocs/op
BenchmarkJsonParserEachKeyStructSmall
BenchmarkJsonParserEachKeyStructSmall-12                 7560410               795 ns/op             192 B/op          8 allocs/op
BenchmarkJsonParserObjectEachStructSmall
BenchmarkJsonParserObjectEachStructSmall-12              9493182               630 ns/op             176 B/op          7 allocs/op
BenchmarkJsonParserSetSmall
BenchmarkJsonParserSetSmall-12                           6147346               976 ns/op             768 B/op          4 allocs/op
BenchmarkJsonParserDelSmall
BenchmarkJsonParserDelSmall-12                           4584642              1307 ns/op               0 B/op          0 allocs/op
PASS
ok      benchmarks      77.529s

Benchmark after change:

goos: darwin
goarch: amd64
pkg: benchmarks
BenchmarkJsonParserLarge
BenchmarkJsonParserLarge-12                               126126             47046 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserMedium
BenchmarkJsonParserMedium-12                              773224              7708 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserDeleteMedium
BenchmarkJsonParserDeleteMedium-12                        689145              8246 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualMedium
BenchmarkJsonParserEachKeyManualMedium-12                1000000              5597 ns/op             112 B/op          2 allocs/op
BenchmarkJsonParserEachKeyStructMedium
BenchmarkJsonParserEachKeyStructMedium-12                 964692              6189 ns/op             560 B/op         12 allocs/op
BenchmarkJsonParserObjectEachStructMedium
BenchmarkJsonParserObjectEachStructMedium-12              761317              7813 ns/op             512 B/op         11 allocs/op
BenchmarkJsonParserSmall
BenchmarkJsonParserSmall-12                              8193255               731 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualSmall
BenchmarkJsonParserEachKeyManualSmall-12                 9560017               627 ns/op              80 B/op          2 allocs/op
BenchmarkJsonParserEachKeyStructSmall
BenchmarkJsonParserEachKeyStructSmall-12                 7580191               795 ns/op             192 B/op          8 allocs/op
BenchmarkJsonParserObjectEachStructSmall
BenchmarkJsonParserObjectEachStructSmall-12              9382509               634 ns/op             176 B/op          7 allocs/op
BenchmarkJsonParserSetSmall
BenchmarkJsonParserSetSmall-12                           6122930               979 ns/op             768 B/op          4 allocs/op
BenchmarkJsonParserDelSmall
BenchmarkJsonParserDelSmall-12                           4542772              1310 ns/op               0 B/op          0 allocs/op
PASS
ok      benchmarks      77.334s

parseInt benchmark before:

goos: darwin
goarch: amd64
pkg: github.com/buger/jsonparser
BenchmarkParseInt
BenchmarkParseInt-12                	173004537	         6.85 ns/op
BenchmarkParseIntUnsafeSlower
BenchmarkParseIntUnsafeSlower-12    	67225647	        17.7 ns/op
BenchmarkParseIntOverflows
BenchmarkParseIntOverflows-12       	221040992	         5.37 ns/op
PASS

parseInt benchmark after:

goos: darwin
goarch: amd64
pkg: github.com/buger/jsonparser
BenchmarkParseInt
BenchmarkParseInt-12                	178624494	         6.70 ns/op
BenchmarkParseIntUnsafeSlower
BenchmarkParseIntUnsafeSlower-12    	65089550	        18.2 ns/op
BenchmarkParseIntOverflows
BenchmarkParseIntOverflows-12       	201364219	         5.93 ns/op
PASS

[buger]

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