output/MultipleOutputs: reduce lock/unlock calls in EnableDisable()

Use ScopeLock to manage the lock; don't unlock after obtaining the
"really_enabled" flag; keep the same lock during EnableWait() /
DisableWait().

src/output/Internal.hxx

@@ -323,13 +323,17 @@ public:
 
 	/**
 	 * Enables the device.
+	 *
+	 * Caller must lock the mutex.
 	 */
-	void LockEnableWait();
+	void EnableWait();
 
 	/**
 	 * Disables the device.
+	 *
+	 * Caller must lock the mutex.
 	 */
-	void LockDisableWait();
+	void DisableWait();
 
 	void LockPauseAsync();
 

src/output/MultipleOutputs.cxx

@@ -44,7 +44,11 @@ MultipleOutputs::MultipleOutputs(MixerListener &_mixer_listener)
 MultipleOutputs::~MultipleOutputs()
 {
 	for (auto i : outputs) {
-		i->LockDisableWait();
+		{
+			const ScopeLock lock(i->mutex);
+			i->DisableWait();
+		}
+
 		i->Finish();
 	}
 }
@@ -107,17 +111,13 @@ void
 MultipleOutputs::EnableDisable()
 {
 	for (auto ao : outputs) {
-		bool enabled;
+		const ScopeLock lock(ao->mutex);
 
-		ao->mutex.lock();
-		enabled = ao->really_enabled;
-		ao->mutex.unlock();
-
-		if (ao->enabled != enabled) {
+		if (ao->enabled != ao->really_enabled) {
 			if (ao->enabled)
-				ao->LockEnableWait();
+				ao->EnableWait();
 			else
-				ao->LockDisableWait();
+				ao->DisableWait();
 		}
 	}
 }

src/output/OutputControl.cxx

@@ -70,7 +70,7 @@ AudioOutput::LockCommandWait(Command cmd)
 }
 
 void
-AudioOutput::LockEnableWait()
+AudioOutput::EnableWait()
 {
 	if (!thread.IsDefined()) {
 		if (plugin.enable == nullptr) {
@@ -84,11 +84,11 @@ AudioOutput::LockEnableWait()
 		StartThread();
 	}
 
-	LockCommandWait(Command::ENABLE);
+	CommandWait(Command::ENABLE);
 }
 
 void
-AudioOutput::LockDisableWait()
+AudioOutput::DisableWait()
 {
 	if (!thread.IsDefined()) {
 		if (plugin.disable == nullptr)
@@ -101,7 +101,7 @@ AudioOutput::LockDisableWait()
 		return;
 	}
 
-	LockCommandWait(Command::DISABLE);
+	CommandWait(Command::DISABLE);
 }
 
 inline bool