first segment is always 0, not an undefined value
regression introduced by aaebd49a
instead of removing the tautology

kills that signed / unsigned comparison warning

The "```" case could also never happen as this is the
decoding of value 0 which should map to mac.

rtp_packetize_split() sets the marker bit according to video semantics,
and uses incorrect timestamp interpolation for PCM.

Opus cannot be fragmented, there must be one frame per RTP packet.

rtp_packetize_common() overrode the correct value with 12, which was
then reset to the correct value.

Note: the AMR packetizer seems odd.

Close #12282
Ref: Debian BTS #762564

stream_Read() can always fail.

fixes 1 byte read overflow

refs #12270