TestRtpStreamSend: ASAN, fix buffer overflow #4689

Job	Run time
ci (ubuntu-20.04, gcc, g++, 20, Release)	7m 49s
ci (ubuntu-20.04, gcc, g++, 20, Debug)	7m 13s
ci (ubuntu-20.04, clang, clang++, 20, Release)	8m 1s
ci (ubuntu-20.04, clang, clang++, 20, Debug)	6m 59s
ci (ubuntu-22.04, gcc, g++, 20, Release)	7m 15s
ci (ubuntu-22.04, gcc, g++, 20, Debug)	6m 46s
ci (ubuntu-22.04, clang, clang++, 20, Release)	8m 56s
ci (ubuntu-22.04, clang, clang++, 20, Debug)	7m 41s
ci (macos-12, gcc, g++, 20, Release)	10m 10s
ci (macos-12, gcc, g++, 20, Debug)	12m 7s
ci (macos-14, clang, clang++, 20, Release)	4m 11s
ci (macos-14, clang, clang++, 20, Debug)	4m 23s
ci (windows-2022, cl, cl, 20, Release)	7m 19s
ci (windows-2022, cl, cl, 20, Debug)	6m 28s
	1h 45m 18s

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