vp8: warn and request sample if upscaling specified in header

Originally committed as revision 23809 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/vp8.c

@@ -399,6 +399,9 @@ static int decode_frame_header(VP8Context *s, const uint8_t *buf, int buf_size)
         buf      += 7;
         buf_size -= 7;
 
+        if (hscale || vscale)
+            av_log_missing_feature(s->avctx, "Upscaling", 1);
+
         s->update_golden = s->update_altref = VP56_FRAME_CURRENT;
         memcpy(s->prob->token    , vp8_token_default_probs , sizeof(s->prob->token));
         memcpy(s->prob->pred16x16, vp8_pred16x16_prob_inter, sizeof(s->prob->pred16x16));