avformat/webpenc: Fix memleak when using invalid packets
The WebP muxer sometimes caches a packet it receives to write it later;
yet if a cached packet is too small (so small as to be invalid),
it is cached, but not written and not unreferenced. Such a packet leaks,
either by being overwritten by the next packet or because it is never
unreferenced at all.
Fix this by not caching unusable packets at all; and error out on
invalid packets.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
projects / ffmpeg / commit