1/0 fix

Originally committed as revision 7658 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263dec.c

@@ -729,7 +729,7 @@ retry:
     decode_slice(s);
     while(s->mb_y<s->mb_height){
         if(s->msmpeg4_version){
-            if(s->mb_x!=0 || (s->mb_y%s->slice_height)!=0 || get_bits_count(&s->gb) > s->gb.size_in_bits)
+            if(s->slice_height==0 || s->mb_x!=0 || (s->mb_y%s->slice_height)!=0 || get_bits_count(&s->gb) > s->gb.size_in_bits)
                 break;
         }else{
             if(ff_h263_resync(s)<0)