lavc: do not leak frames in avcodec_decode_audio4

Notwithstanding the return value the frame should be freed if
is not going to be used.
Reported-by: Matthew Wolenetz <wolenetz@chromium.org>

libavcodec/utils.c

@@ -1463,9 +1463,7 @@ int attribute_align_arg avcodec_decode_audio4(AVCodecContext *avctx,
                 frame->extended_buf    = NULL;
                 frame->nb_extended_buf = 0;
             }
-        }
-
-        if (ret < 0 && frame->data[0])
+        } else if (frame->data[0])
             av_frame_unref(frame);
     }