x11: Always update the borders on frame extent events

Always update the border sizes on frame extent events, or they can incorrectly still be zero if followed by a PropertyNotify event when leaving fullscreen.

Fixes sending the correct restored window size when leaving fullscreen in fvwm.

(cherry picked from commit 0ac1241b7a5cd5d0dc318f26cfdbb9672564404b)

src/video/x11/SDL_x11events.c

@@ -1513,9 +1513,10 @@ static void X11_DispatchEvent(SDL_VideoDevice *_this, XEvent *xevent)
                                       &ChildReturn);
         }
 
-        /* Xfce sends ConfigureNotify before PropertyNotify when toggling fullscreen and maximized, which
-         * is backwards from every other window manager, as well as what is expected by SDL and its clients.
-         * Defer emitting the size/move events until the corresponding PropertyNotify arrives.
+        /* Some window managers send ConfigureNotify before PropertyNotify when changing state (Xfce and
+         * fvwm are known to do this), which is backwards from other window managers, as well as what is
+         * expected by SDL and its clients. Defer emitting the size/move events until the corresponding
+         * PropertyNotify arrives for consistency.
          */
         const Uint32 changed = X11_GetNetWMState(_this, data->window, xevent->xproperty.window) ^ data->window->flags;
         if (changed & (SDL_WINDOW_FULLSCREEN | SDL_WINDOW_MAXIMIZED)) {
@@ -1950,13 +1951,12 @@ static void X11_DispatchEvent(SDL_VideoDevice *_this, XEvent *xevent)
                right approach, but it seems to work. */
             X11_UpdateKeymap(_this, true);
         } else if (xevent->xproperty.atom == videodata->atoms._NET_FRAME_EXTENTS) {
-            /* Events are disabled when leaving fullscreen until the borders appear to avoid
-             * incorrect size/position events.
-             */
+            X11_GetBorderValues(data);
             if (data->size_move_event_flags) {
+                /* Events are disabled when leaving fullscreen until the borders appear to avoid
+                 * incorrect size/position events on compositing window managers.
+                 */
                 data->size_move_event_flags &= ~X11_SIZE_MOVE_EVENTS_WAIT_FOR_BORDERS;
-                X11_GetBorderValues(data);
-
             }
             if (!(data->window->flags & SDL_WINDOW_FULLSCREEN) && data->toggle_borders) {
                 data->toggle_borders = false;