x11: Ensure that a configure event was received before sending the final window size and coordinates

Headless display servers might not send an initial configure event, so don't assume that one has arrived and send garbage size/position values when showing a window.

src/video/x11/SDL_x11window.c

@@ -1369,18 +1369,23 @@ void X11_ShowWindow(SDL_VideoDevice *_this, SDL_Window *window)
     X11_XSync(display, False);
     X11_PumpEvents(_this);
 
-    int x = data->last_xconfigure.x;
-    int y = data->last_xconfigure.y;
-    SDL_GlobalToRelativeForWindow(data->window, x, y, &x, &y);
+    /* If a configure event was received (type is non-zero), send the final window size and coordinates. */
+    if (data->last_xconfigure.type) {
+        int x = data->last_xconfigure.x;
+        int y = data->last_xconfigure.y;
+        SDL_GlobalToRelativeForWindow(data->window, x, y, &x, &y);
 
-    /* If the borders appeared, this happened automatically in the event system, otherwise, set the position now. */
-    if (data->disable_size_position_events && (window->x != x || window->y != y)) {
-        data->pending_operation = X11_PENDING_OP_MOVE;
-        X11_XMoveWindow(display, data->xwindow, window->x, window->y);
+        /* If the borders appeared, this happened automatically in the event system, otherwise, set the position now. */
+        if (data->disable_size_position_events && (window->x != x || window->y != y)) {
+            data->pending_operation = X11_PENDING_OP_MOVE;
+            X11_XMoveWindow(display, data->xwindow, window->x, window->y);
+        }
+
+        SDL_SendWindowEvent(window, SDL_EVENT_WINDOW_RESIZED, data->last_xconfigure.width, data->last_xconfigure.height);
+        SDL_SendWindowEvent(window, SDL_EVENT_WINDOW_MOVED, x, y);
     }
+
     data->disable_size_position_events = SDL_FALSE;
-    SDL_SendWindowEvent(window, SDL_EVENT_WINDOW_RESIZED, data->last_xconfigure.width, data->last_xconfigure.height);
-    SDL_SendWindowEvent(window, SDL_EVENT_WINDOW_MOVED, x, y);
 }
 
 void X11_HideWindow(SDL_VideoDevice *_this, SDL_Window *window)