avcodec/jacosubdec: check strftime return value

Fixes CID1257004
avdevice/xcbgrab: Fix show_region rectangle

Fixes trac ticket #4164

This is to address an error when using show_region, which would cause part of the captured area to become static.
It looks like the rectangle specifying the capture area was relative to the capture window.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/utils: Check AVFrame width/height in avcodec_encode_video2()

This is similar to the format check

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