Merge commit '90411b333d6b6bb69d8937117b9250785730dc53'

* commit '90411b333d6b6bb69d8937117b9250785730dc53':
  Allow reading of growing avi files (currently being written)

Conflicts:
	libavformat/avidec.c
	tests/ref/fate/cvid-partial

See: e42a3dd123
Merged-by: Michael Niedermayer <michaelni@gmx.at>