Regression introduced in [c75dafab]
Bug spotted by Fabio Ritrovato

for in english code)

a bit later ... but at least it gives a starting point for people
wanting to have fun with transcode / audio / filter chains)

less than that of the planar version (uses nearest neighboor instead of
interpolated colors)

Fixes a bunch of crashes at exit.

It needs to be done by the parent (VLM or playlist)

vlc_threadobj() is no use otherwise. People may want not to enable
reference checking all the time also...

with an ugly green in packed YUV).