ffmpeg: Clean up if filter initialisation failed to avoid a memleak.

Fixes ticket #3858.

Reviewed-by: Nicolas George
lavf/rtpdec_hevc: Fix compilation with -DDEBUG.
proresenc_ks: allow auto-selecting profile

The user may not know how to select the profile, nor what he needs, in
particular to encode alpha.

Therefore, use an automatic selection as default, and warn when the
manually selected profile may cause issues.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'cehoyos/master'

* cehoyos/master:
  lavf/rtpdec_hevc: Fix compilation with -DDEBUG.
  ffmpeg: Clean up if filter initialisation failed to avoid a memleak.

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