event/MaskMonitor: add `noexcept`

src/event/MaskMonitor.cxx

 /*
- * Copyright 2003-2018 The Music Player Daemon Project
+ * Copyright 2003-2019 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -20,7 +20,7 @@
 #include "MaskMonitor.hxx"
 
 void
-MaskMonitor::OrMask(unsigned new_mask)
+MaskMonitor::OrMask(unsigned new_mask) noexcept
 {
 	if (pending_mask.fetch_or(new_mask) == 0)
 		defer.Schedule();

src/event/MaskMonitor.hxx

@@ -40,19 +40,19 @@ class MaskMonitor final {
 	std::atomic_uint pending_mask;
 
 public:
-	MaskMonitor(EventLoop &_loop, Callback _callback)
+	MaskMonitor(EventLoop &_loop, Callback _callback) noexcept
 		:defer(_loop, BIND_THIS_METHOD(RunDeferred)),
 		 callback(_callback), pending_mask(0) {}
 
-	EventLoop &GetEventLoop() {
+	EventLoop &GetEventLoop() noexcept {
 		return defer.GetEventLoop();
 	}
 
-	void Cancel() {
+	void Cancel() noexcept {
 		defer.Cancel();
 	}
 
-	void OrMask(unsigned new_mask);
+	void OrMask(unsigned new_mask) noexcept;
 
 protected:
 	/* DeferEvent callback */