output/MultipleOutputs: add method HasName()

src/output/MultipleOutputs.cxx

@@ -98,7 +98,7 @@ MultipleOutputs::Configure(EventLoop &event_loop,
 						mixer_listener,
 						client, block, defaults,
 						&filter_factory);
-		if (FindByName(output->GetName()) != nullptr)
+		if (HasName(output->GetName()))
 			throw FormatRuntimeError("output devices with identical "
 						 "names: %s", output->GetName());
 

src/output/MultipleOutputs.hxx

@@ -113,6 +113,14 @@ public:
 	gcc_pure
 	AudioOutputControl *FindByName(const char *name) noexcept;
 
+	/**
+	 * Does an audio output device with this name exist?
+	 */
+	gcc_pure
+	bool HasName(const char *name) noexcept {
+		return FindByName(name) != nullptr;
+	}
+
 	void SetReplayGainMode(ReplayGainMode mode) noexcept;
 
 	/**