This was already done when SPS or PPS NALUs were found with the same
ID as active SPS or PPS but with different content. The missing case
were SPS or PPS NALUs whose IDs hadn't been seen before.
After such an encounter all following key frames must be prepended
with the active SPS & PPS, too. Otherwise seeking would not work as
the player only used the SPS & PPS from CodecPrivate but didn't know
about the new ones from mid-stream.
Part of the fix of #2250.
