Invalid pointer casting in H264 packetizer

[ray1422]

This causes runtime error when sanitizer is enabled since vector is not aligned to 4, and uint32_t requires 4 bytes alignment.

https://github.com/paullouisageneau/libdatachannel/blob/master/src/h264rtppacketizer.cpp#L36C4-L36C10

[ray1422]

reproduce steps

1. Enable sanitizers

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=address -fsanitize=undefined -fsanitize=leak")

2. compile with g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
3. run streamer example

errors:
libdatachannel/examples/streamer/h264fileparser.cpp:32:32: runtime error: load of misaligned address 0x63200000081d for type 'unsigned int', which requires 4 byte alignment

/workspaces/libdatachannel/src/h264rtppacketizer.cpp:36:36
libdatachannel/src/h264rtppacketizer.cpp:36:36: runtime error: load of misaligned address 0x63200006081d for type 'unsigned int', which requires 4 byte alignment

[ray1422]

#1157

[paullouisageneau]

Thank you for reporting and fixing the issue!