mlpdec: fix request_channel_layout behavior.

When request_channel_layout is 0,
all substreams should be decoded.
Signed-off-by: Tim Walker <tdskywalker@gmail.com>

libavcodec/mlpdec.c

@@ -504,7 +504,7 @@ FF_DISABLE_DEPRECATION_WARNINGS
     } else
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
-    if ((s->ch_layout & m->avctx->request_channel_layout) ==
+    if (m->avctx->request_channel_layout && (s->ch_layout & m->avctx->request_channel_layout) ==
         m->avctx->request_channel_layout && m->max_decoded_substream > substr) {
         av_log(m->avctx, AV_LOG_DEBUG,
                "Extracting %d-channel downmix (0x%"PRIx64") from substream %d. "