Merge commit '3735b5c616770429572f86aabdaec39c6ebb8818'

* commit '3735b5c616770429572f86aabdaec39c6ebb8818':
  Revert "lavfi: always check av_expr_parse_and_eval() return value"

See: 8c9a23833daa88bdf08b7e7fbf3a64ab689ad373
Merged-by: Michael Niedermayer <michaelni@gmx.at>