Make sure avcodec_set_dimensions() is used when rv20 changes resolution.

This should fix lowres resolution changes.

Originally committed as revision 20589 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/rv10.c

@@ -370,8 +370,9 @@ static int rv20_decode_picture_header(MpegEncContext *s)
             if (avcodec_check_dimensions(s->avctx, new_h, new_w) < 0)
                 return -1;
             MPV_common_end(s);
-            s->width  = s->avctx->width = new_w;
-            s->height = s->avctx->height= new_h;
+            avcodec_set_dimensions(s->avctx, new_w, new_h);
+            s->width  = new_w;
+            s->height = new_h;
             if (MPV_common_init(s) < 0)
                 return -1;
         }