Merge commit 'f4281f45'

* commit 'f4281f45':
  asrc_anullsrc: do not set samplerate and channel layout explicitly

Conflicts:
	libavfilter/asrc_anullsrc.c

No change to FFmpeg due to semantic difference between the filter sources
Merged-by: NMichael Niedermayer <michaelni@gmx.at>