output/Control: move pipe initialization to the OutputThread

Un-protect the SharedPipeConsumer instance, and make it available in
the OutputThread only.  This gives more well-defined mutex protection.

src/output/Internal.hxx

@@ -256,6 +256,11 @@ struct AudioOutput {
 		 * The #AudioFormat requested by #Command::OPEN.
 		 */
 		AudioFormat audio_format;
+
+		/**
+		 * The #MusicPipe passed to #Command::OPEN.
+		 */
+		const MusicPipe *pipe;
 	} request;
 
 	/**

src/output/OutputControl.cxx

@@ -122,8 +122,7 @@ AudioOutput::Open(const AudioFormat audio_format, const MusicPipe &mp)
 	}
 
 	request.audio_format = audio_format;
-
+	request.pipe = ∓
-	pipe.Init(mp);
 
 	if (!thread.IsDefined())
 		StartThread();

src/output/OutputThread.cxx

@@ -145,6 +145,7 @@ AudioOutput::Open()
 		return;
 
 	in_audio_format = request.audio_format;
+	pipe.Init(*request.pipe);
 
 	bool success;
 
@@ -284,8 +285,9 @@ AudioOutput::Reopen()
 {
 	assert(open);
 
-	if (request.audio_format != in_audio_format &&
+	if ((request.audio_format != in_audio_format &&
-	    !config_audio_format.IsFullyDefined()) {
+	     !config_audio_format.IsFullyDefined()) ||
+	    request.pipe != &pipe.GetPipe()) {
 		Close(true);
 		Open();
 	} else {