event/SocketEvent: allow Close() without socket

src/event/ServerSocket.cxx

@@ -75,8 +75,7 @@ public:
 	OneServerSocket &operator=(const OneServerSocket &other) = delete;
 
 	~OneServerSocket() noexcept {
-		if (IsDefined())
-			Close();
+		Close();
 	}
 
 	[[nodiscard]] unsigned GetSerial() const noexcept {

src/event/SocketEvent.cxx

@@ -50,6 +50,9 @@ SocketEvent::Steal() noexcept
 void
 SocketEvent::Close() noexcept
 {
+	if (!fd.IsDefined())
+		return;
+
 	Steal().Close();
 }