Fix OOB access in mpeg4/h263 decoder

The decoder does not support an increase in frame width, and
would exceed its buffer if the width increased mid-stream.
There was an existing check to prevent the total frame size
(width*height) from increasing, but in fact the decoder also
does not even support a width increase, even if the height
decreases correspondingly.

Bug: 136175447
Bug: 136173699
Test: manual
Change-Id: Ic2d28bb0503635dadeb69ba3be9412d58684e910
(cherry picked from commit ef4ce157)