dvdsub_parse_extradata: fix memleak

Fixes CID1135765
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/g2meet: check the return code of ff_set_dimensions()

This is currently redundant as the checks before it are tighter than
the checks in ff_set_dimensions() but its more robust not to depend
on that.

Fixes CID1135739
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>