indeo: Check allocated tile size in ff_ivi_process_empty_tile()

This prevents writing into a too small array if some parameters changed
without the tile being reallocated.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/ivi_common.c

@@ -486,6 +486,12 @@ void ff_ivi_process_empty_tile(AVCodecContext *avctx, IVIBandDesc *band,
     void (*mc_no_delta_func)(int16_t *buf, const int16_t *ref_buf, uint32_t pitch,
                              int mc_type);
 
+    if( tile->num_MBs != IVI_MBs_PER_TILE(tile->width, tile->height, band->mb_size) ){
+        av_log(avctx, AV_LOG_ERROR, "allocated tile size %d mismatches parameters %d in ff_ivi_process_empty_tile()\n",
+               tile->num_MBs, IVI_MBs_PER_TILE(tile->width, tile->height, band->mb_size));
+        return;
+    }
+
     offs       = tile->ypos * band->pitch + tile->xpos;
     mb         = tile->mbs;
     ref_mb     = tile->ref_mbs;