h264: Fix assignments in if()

Fixes null pointer dereference later, since if this function failed,
a positive return value was returned to the caller.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Martin Storsjö <martin@martin.st>
lavc: Fix assignments in if() when calling ff_af_queue_add

Signed-off-by: Martin Storsjö <martin@martin.st>
svq1enc: Fix assignments in if()

Signed-off-by: Martin Storsjö <martin@martin.st>
lavf: Fix assignments in if()

Signed-off-by: Martin Storsjö <martin@martin.st>
rtmpproto: Fix assignments in if()

Signed-off-by: Martin Storsjö <martin@martin.st>