mlp_parser: fix request_channel_layout behavior.

When request_channel_layout is 0,
all substreams should be decoded.

Thanks to Michael Niedermayer for spotting.

Also fix a mismatch between the parser and
decoder when request_channel_layout is a
subset of Stereo.

libavcodec/mlp_parser.c

@@ -335,7 +335,9 @@ FF_DISABLE_DEPRECATION_WARNINGS
             } else
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
-            if (avctx->request_channel_layout == AV_CH_LAYOUT_STEREO &&
+            if (avctx->request_channel_layout &&
+                (avctx->request_channel_layout & AV_CH_LAYOUT_STEREO) ==
+                avctx->request_channel_layout &&
                 mh.num_substreams > 1) {
                 avctx->channels       = 2;
                 avctx->channel_layout = AV_CH_LAYOUT_STEREO;
@@ -358,13 +360,16 @@ FF_DISABLE_DEPRECATION_WARNINGS
             } else
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
-            if (avctx->request_channel_layout == AV_CH_LAYOUT_STEREO &&
-                mh.num_substreams > 1) {
+                if (avctx->request_channel_layout &&
+                    (avctx->request_channel_layout & AV_CH_LAYOUT_STEREO) ==
+                    avctx->request_channel_layout &&
+                    mh.num_substreams > 1) {
                 avctx->channels       = 2;
                 avctx->channel_layout = AV_CH_LAYOUT_STEREO;
             } else if (!mh.channels_thd_stream2 ||
-                       (mh.channel_layout_thd_stream1 & avctx->request_channel_layout) ==
-                       avctx->request_channel_layout) {
+                       (avctx->request_channel_layout &&
+                        (avctx->request_channel_layout & mh.channel_layout_thd_stream1) ==
+                        avctx->request_channel_layout)) {
                 avctx->channels       = mh.channels_thd_stream1;
                 avctx->channel_layout = mh.channel_layout_thd_stream1;
             } else {