Merge commit 'f935aca4'

* commit 'f935aca4':
  av_memcpy_backptr: avoid an infinite loop for back = 0
  4xm: check the return value of read_huffman_tables().

Conflicts:
	libavcodec/4xm.c
	libavutil/mem.c

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