event/SocketEvent: allow Cancel() without socket

src/event/SocketEvent.cxx

@@ -38,12 +38,6 @@ SocketEvent::Dispatch() noexcept
 		callback(flags);
 }
 
-SocketEvent::~SocketEvent() noexcept
-{
-	if (IsDefined())
-		Cancel();
-}
-
 void
 SocketEvent::Open(SocketDescriptor _fd) noexcept
 {
@@ -72,11 +66,11 @@ SocketEvent::Close() noexcept
 bool
 SocketEvent::Schedule(unsigned flags) noexcept
 {
-	assert(IsDefined());
-
 	if (flags == GetScheduledFlags())
 		return true;
 
+	assert(IsDefined());
+
 	bool success;
 	if (scheduled_flags == 0)
 		success = loop.AddFD(fd.Get(), flags, *this);

src/event/SocketEvent.hxx

@@ -91,7 +91,9 @@ public:
 		 callback(_callback),
 		 fd(_fd) {}
 
-	~SocketEvent() noexcept;
+	~SocketEvent() noexcept {
+		Cancel();
+	}
 
 	auto &GetEventLoop() const noexcept {
 		return loop;

src/lib/dbus/Watch.cxx

@@ -52,8 +52,7 @@ DbusToLibevent(unsigned flags) noexcept
 void
 WatchManager::Watch::Toggled() noexcept
 {
-	if (event.IsDefined())
-		event.Cancel();
+	event.Cancel();
 
 	if (dbus_watch_get_enabled(&watch)) {
 		event.Open(SocketDescriptor(dbus_watch_get_unix_fd(&watch)));