avcodec/ivi: Fix segfault on allocation error

If allocating the tiles array for indeo 4/5 fails, the context is in an
inconsistent state, because the counter for the number of tiles is > 0.
This will lead to a segfault when freeing the tiles' substructures.
Fix this by setting the number of tiles to zero if the allocation was
unsuccessful.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit e411a3af11)

libavcodec/ivi.c

@@ -442,8 +442,10 @@ av_cold int ff_ivi_init_tiles(IVIPlaneDesc *planes,
 
             av_freep(&band->tiles);
             band->tiles = av_mallocz_array(band->num_tiles, sizeof(IVITile));
-            if (!band->tiles)
+            if (!band->tiles) {
+                band->num_tiles = 0;
                 return AVERROR(ENOMEM);
+            }
 
             /* use the first luma band as reference for motion vectors
              * and quant */