Draft: packetizer/decoder: no longer handle corruption as discontinuity

Corrupted packets are flagged when a block has been created with truncated end, or lost packet after the start.

There's no reason to reset time base or codec parameters when received a corrupted packet.

Drain on corruption also doesn't help as, for example, video codecs with reference frames will still output corrupted frames from missing references.

What should be done depends on codec.