avcodec/h263dec: Reinitialize idct context if it has not been setup for the active profile

The profile after reading headers can be different from when the context was initialized
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/h263dec.c

@@ -546,6 +546,8 @@ retry:
     if (CONFIG_MPEG4_DECODER && avctx->codec_id == AV_CODEC_ID_MPEG4) {
         if (ff_mpeg4_workaround_bugs(avctx) == 1)
             goto retry;
+        if (s->studio_profile != (s->idsp.idct == NULL))
+            ff_mpv_idct_init(s);
     }
 
     /* After H.263 & MPEG-4 header decode we have the height, width,