vp56dec: avoid freeing the returned frame before returning it.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vp56.c

@@ -621,7 +621,7 @@ int ff_vp56_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
 
     next:
         if (p->key_frame || golden_frame) {
-            if (s->framep[VP56_FRAME_GOLDEN]->data[0] &&
+            if (s->framep[VP56_FRAME_GOLDEN]->data[0] && s->framep[VP56_FRAME_GOLDEN] != p &&
                 s->framep[VP56_FRAME_GOLDEN] != s->framep[VP56_FRAME_GOLDEN2])
                 avctx->release_buffer(avctx, s->framep[VP56_FRAME_GOLDEN]);
             s->framep[VP56_FRAME_GOLDEN] = p;