playlist: Give PlaylistQueues a clear() function

This is used to clear the queue before populating it with a different
playlist.

Signed-off-by: Anna Schumaker <Anna@OcarinaProject.net>

core/playlist.cpp

@@ -17,13 +17,17 @@ public:
 		set_flag(Q_NO_SORT);
 	}
 
+	void clear()
+	{
+		while (size() > 0)
+			del((unsigned)0);
+	}
+
 	void fill(IndexEntry *ent)
 	{
 		std::set<unsigned int>::iterator it;
 
-		while (size() > 0)
-			del((unsigned)0);
-
+		clear();
 		for (it = ent->begin(); it != ent->end(); it++)
 			add(tags :: get_track(*it));
 	}