lavfi/buffersink: factor checks for lists sizes.
lavu: add av_pure to av_int_list_length_for_size.
lavu: add parens to macro argument.
lavu/opt: check int lists length for overflow.

Also add parens on macro arguments.
Merge remote-tracking branch 'cigaes/master'

* cigaes/master:
  lavu/opt: check int lists length for overflow.
  lavu: add parens to macro argument.
  lavu: add av_pure to av_int_list_length_for_size.
  lavfi/buffersink: factor checks for lists sizes.

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