avfilter: Silence warning: passing argument 3 of av_image_copy from incompatible pointer type

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
vf_overlay: silence warning: X may be used uninitialized in this function

Also ensure that format is valid in query_formats

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
aacdec: Fix warning: initialization from incompatible pointer type

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