event/TimerEvent: assign `due` in Schedule()

src/event/Loop.cxx

@@ -152,11 +152,10 @@ EventLoop::AbandonFD(SocketEvent &event)  noexcept
 }
 
 void
-EventLoop::AddTimer(TimerEvent &t, Event::Duration d) noexcept
+EventLoop::Insert(TimerEvent &t) noexcept
 {
 	assert(IsInside());
 
-	t.due = SteadyNow() + d;
 	timers.insert(t);
 	again = true;
 }

src/event/Loop.hxx

@@ -214,7 +214,7 @@ public:
 	 */
 	bool AbandonFD(SocketEvent &event) noexcept;
 
-	void AddTimer(TimerEvent &t, Event::Duration d) noexcept;
+	void Insert(TimerEvent &t) noexcept;
 
 	/**
 	 * Schedule a call to DeferEvent::RunDeferred().

src/event/TimerEvent.cxx

@@ -25,12 +25,22 @@ TimerEvent::Schedule(Event::Duration d) noexcept
 {
 	Cancel();
 
-	loop.AddTimer(*this, d);
+	due = loop.SteadyNow() + d;
+	loop.Insert(*this);
 }
 
 void
 TimerEvent::ScheduleEarlier(Event::Duration d) noexcept
 {
-	if (!IsPending() || loop.SteadyNow() + d < due)
-		Schedule(d);
+	const auto new_due = loop.SteadyNow() + d;
+
+	if (IsPending()) {
+		if (new_due >= due)
+			return;
+
+		Cancel();
+	}
+
+	due = new_due;
+	loop.Insert(*this);
 }