hevc: Initialize sample aspect to valid value.

Without this, it is 0/0 by default, which is not allowed.
This sets it to 0/1, which means "undefined".

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
avcodec/vp9: Add asserts to help source code analyzers

See CID1108596 and CID1108595
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/au: add assert to help source code analyzers

See: CID1108585 and CID1108603
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>