Revert "avformat/utils: Close codec context since it is allocated by avformat_new_stream in refrence to ticket 2716"

This causes a race condition with VLC. Its plausible that other
applications also would have races with it and its just fixing a memleak when
the user application forgets to free the codec. It causes more
problems than it solves in its current form, thus the revert.
Better solutions are welcome

This reverts commit 0f229f9b91fe3c4ebd97e88f004d638819b76add.
avcodec/h264_sei/ff_h264_decode_sei: fix error codes for insufficient data

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/ff_h264_decode_sei: fix integer overflow with size.

This issue is hypothetical and no testcase is available.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/ff_h264_decode_sei: Check SEI size

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/ff_h264_decode_sei: use skip_bits_long()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>