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

media/libstagefright/codecs/m4v_h263/dec/src/vop.cpp

@@ -1355,6 +1355,14 @@ PV_STATUS DecodeShortHeader(VideoDecData *video, Vop *currVop)
             int tmpHeight = (tmpDisplayHeight + 15) & -16;
             int tmpWidth = (tmpDisplayWidth + 15) & -16;
 
+            if (tmpWidth > video->width)
+            {
+                // while allowed by the spec, this decoder does not actually
+                // support an increase in size.
+                ALOGE("width increase not supported");
+                status = PV_FAIL;
+                goto return_point;
+            }
             if (tmpHeight * tmpWidth > video->size)
             {
                 // This is just possibly "b/37079296".