avcodec/vp3: Do not return random positive values but the buf size

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit d8094a303b)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/vp3.c

@@ -2014,16 +2014,18 @@ static int vp3_decode_frame(AVCodecContext *avctx,
                 ret = vp3_decode_init(avctx);
             if (ret < 0) {
                 vp3_decode_end(avctx);
+                return ret;
             }
-            return ret;
+            return buf_size;
         } else if (type == 2) {
             ret = theora_decode_tables(avctx, &gb);
             if (ret >= 0)
                 ret = vp3_decode_init(avctx);
             if (ret < 0) {
                 vp3_decode_end(avctx);
+                return ret;
             }
-            return ret;
+            return buf_size;
         }
 
         av_log(avctx, AV_LOG_ERROR,