Fixed register_window_classcreate_window_class

First, try to unregister previously registered class.

src/osd/windows/output.c

@@ -171,6 +171,8 @@ static int create_window_class(void)
 		wc.lpszClassName    = OUTPUT_WINDOW_CLASS;
 		wc.hInstance        = GetModuleHandleUni();
 		wc.lpfnWndProc      = output_window_proc;
+		
+		UnregisterClass(wc.lpszClassName, wc.hInstance);
 
 		// register the class; fail if we can't
 		if (!RegisterClass(&wc))