TestRtpStreamSend: ASAN, fix buffer overflow #4691

Job	Run time
ci (ubuntu-20.04, gcc, g++, 20, Release)	7m 51s
ci (ubuntu-20.04, gcc, g++, 20, Debug)	7m 24s
ci (ubuntu-20.04, clang, clang++, 20, Release)	7m 59s
ci (ubuntu-20.04, clang, clang++, 20, Debug)	7m 0s
ci (ubuntu-22.04, gcc, g++, 20, Release)	7m 28s
ci (ubuntu-22.04, gcc, g++, 20, Debug)	7m 24s
ci (ubuntu-22.04, clang, clang++, 20, Release)	8m 42s
ci (ubuntu-22.04, clang, clang++, 20, Debug)	8m 44s
ci (macos-12, gcc, g++, 20, Release)	8m 20s
ci (macos-12, gcc, g++, 20, Debug)	13m 18s
ci (macos-14, clang, clang++, 20, Release)	5m 39s
ci (macos-14, clang, clang++, 20, Debug)	4m 43s
ci (windows-2022, cl, cl, 20, Release)	7m 32s
ci (windows-2022, cl, cl, 20, Debug)	6m 7s
	1h 48m 11s

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