Merge commit '7ab551f9'

* commit '7ab551f9':
  h264: prevent theoretical infinite loop in SEI parsing

Conflicts:
	libavcodec/h264_sei.c

Not merged, as this would remove 2 bitstream compliance checks.
The specification does not allow the bitstream to end in the middle
of these variable length elements and we have no samples which
have such non compliant truncation either so its better to error
out. Which is simpler as well

This issue also has been fixed long ago
See: 9decfc17Merged-by: Michael Niedermayer <michaelni@gmx.at>