MusicPipe: disallow copying

src/MusicPipe.hxx

@@ -59,6 +59,8 @@ public:
 	 */
 	MusicPipe() = default;
 
+	MusicPipe(const MusicPipe &) = delete;
+
 	/**
 	 * Frees the object.  It must be empty now.
 	 */
@@ -67,6 +69,8 @@ public:
 		assert(tail_r == &head);
 	}
 
+	MusicPipe &operator=(const MusicPipe &) = delete;
+
 #ifndef NDEBUG
 	/**
 	 * Checks if the audio format if the chunk is equal to the specified