chromecast: Include music metadata

Music related metadata like album, albumartist, tracknumber and
discnumber is currently not added to media playback messages for
Chromecast.

This patch will add the entries if they're specified in the media
metadata.

modules/stream_out/chromecast/chromecast_communication.cpp

@@ -327,13 +327,13 @@ std::string ChromecastCommunication::GetMedia( const std::string& mime,
             {
                 if( !artist.empty() )
                     ss << ",\"artist\":\"" << artist << "\"";
-                if( album.empty() )
+                if( !album.empty() )
                     ss << ",\"album\":\"" << album << "\"";
-                if( albumartist.empty() )
+                if( !albumartist.empty() )
                     ss << ",\"albumArtist\":\"" << albumartist << "\"";
-                if( tracknumber.empty() )
+                if( !tracknumber.empty() )
                     ss << ",\"trackNumber\":\"" << tracknumber << "\"";
-                if( discnumber.empty() )
+                if( !discnumber.empty() )
                     ss << ",\"discNumber\":\"" << discnumber << "\"";
             }