playlist: added playlist_get_queue()

To allow code outside playlist.c to access the "queue" object,
provide a function which returns a const pointer.

src/playlist.c

@@ -132,6 +132,12 @@ void finishPlaylist(void)
 	g_rand = NULL;
 }
 
+const struct queue *
+playlist_get_queue(void)
+{
+	return &playlist.queue;
+}
+
 void clearPlaylist(void)
 {
 	stopPlaylist();

src/playlist.h

@@ -94,6 +94,12 @@ void initPlaylist(void);
 
 void finishPlaylist(void);
 
+/**
+ * Returns the "queue" object of the global playlist instance.
+ */
+const struct queue *
+playlist_get_queue(void);
+
 void readPlaylistState(FILE *);
 
 void savePlaylistState(FILE *);