avcodec/libvpxdec: Check that display dimensions fit in the storage dimensions

Fixes assertion failure
Fixes: 2112/clusterfuzz-testcase-minimized-4526878557732864

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
