TestRtpStreamSend: ASAN, fix buffer overflow #4690

Job	Run time
ci (ubuntu-20.04, gcc, g++, 20, Release)	7m 49s
ci (ubuntu-20.04, gcc, g++, 20, Debug)	7m 28s
ci (ubuntu-20.04, clang, clang++, 20, Release)	8m 1s
ci (ubuntu-20.04, clang, clang++, 20, Debug)	7m 4s
ci (ubuntu-22.04, gcc, g++, 20, Release)	7m 7s
ci (ubuntu-22.04, gcc, g++, 20, Debug)	6m 42s
ci (ubuntu-22.04, clang, clang++, 20, Release)	9m 1s
ci (ubuntu-22.04, clang, clang++, 20, Debug)	7m 42s
ci (macos-12, gcc, g++, 20, Release)	12m 21s
ci (macos-12, gcc, g++, 20, Debug)	8m 51s
ci (macos-14, clang, clang++, 20, Release)	6m 30s
ci (macos-14, clang, clang++, 20, Debug)	4m 18s
ci (windows-2022, cl, cl, 20, Release)	7m 12s
ci (windows-2022, cl, cl, 20, Debug)	5m 30s
	1h 45m 36s

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