lavfi/overlay: correct small error in intersection detection

The image size of the destination image was used to determine if a source
image was positioned outside the destination image, that no intersection
could occur.  Actually for these two cases the size of the source image
has to be used!

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
avcodec/x86/videodsp: fix a bug in a %if statement where we used '%%' instead of '&&'.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/x86/videodsp: Small speedups in ff_emulated_edge_mc x86 SIMD.

Don't use word-size multiplications if size == 2, and if we're using
SIMD instructions (size >= 8), complete leftover 4byte sets using movd,
not mov. Both of these changes lead to minor speedups.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
vp9: skip itxfm_add if the whole block has no coefficients.

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