x11: Don't block when withdrawing unmapped windows

Some window managers will mark minimized or offscreen windows as unmapped. When hiding a window, unconditionally call XWithdrawWindow, and don't wait for an UnmapNotify event if the window is already in the unmapped state, or it will block indefinitely waiting for an event that never arrives.

src/video/x11/SDL_x11window.c

@@ -1642,14 +1642,16 @@ void X11_HideWindow(SDL_VideoDevice *_this, SDL_Window *window)
     Display *display = data->videodata->display;
     XEvent event;
 
-    if (X11_IsWindowMapped(_this, window)) {
-        X11_XWithdrawWindow(display, data->xwindow, screen);
-        // Blocking wait for "UnmapNotify" event
-        if (!(window->flags & SDL_WINDOW_EXTERNAL) && X11_IsDisplayOk(display)) {
-            X11_XIfEvent(display, &event, &isUnmapNotify, (XPointer)&data->xwindow);
-        }
-        X11_XFlush(display);
+    /* Some window managers will mark minimized or offscreen windows as unmapped, so we
+     * must not block while waiting for an UnmapNotify event that will never arrive.
+     */
+    const bool is_mapped = X11_IsWindowMapped(_this, window);
+    X11_XWithdrawWindow(display, data->xwindow, screen);
+    if (is_mapped && !(window->flags & SDL_WINDOW_EXTERNAL) && X11_IsDisplayOk(display)) {
+        // Blocking wait for "UnmapNotify" event.
+        X11_XIfEvent(display, &event, &isUnmapNotify, (XPointer)&data->xwindow);
     }
+    X11_XFlush(display);
 
     // Transfer keyboard focus back to the parent
     if ((window->flags & SDL_WINDOW_POPUP_MENU) && !(window->flags & SDL_WINDOW_NOT_FOCUSABLE)) {