win32: make a flag explicit

This shouldn't change anything. But it's worth making this explicit,
since it's very subtle and unintuitive: if the X parameter is the
magic value CW_USEDEFAULT, then the Y parameter is used as nCmdShow
parameter to ShowWindow(). And in our case, this is SW_HIDE (0),
because we want to create a hidden window.

video/out/w32_common.c

@@ -950,7 +950,7 @@ int vo_w32_init(struct vo *vo)
         w32->window = CreateWindowExW(0, classname,
                                       classname,
                                       update_style(w32, 0),
-                                      CW_USEDEFAULT, 0, 100, 100,
+                                      CW_USEDEFAULT, SW_HIDE, 100, 100,
                                       0, 0, hInstance, w32);
     }