If the client rect is empty, use the last known window size

This happens on Windows 11 with fullscreen desktop windows when the desktop is brought up with the Windows+D shortcut.

Fixes https://github.com/libsdl-org/SDL/issues/7419

(cherry picked from commit 2ca727aec6f5f264620f80999beb5ef77eefec4a)

src/video/windows/SDL_windowsevents.c

@@ -1349,8 +1349,7 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                 RECT rect;
                 float x, y;
 
-                if (!GetClientRect(hwnd, &rect) ||
-                    (rect.right == rect.left && rect.bottom == rect.top)) {
+                if (!GetClientRect(hwnd, &rect) || IsRectEmpty(&rect)) {
                     if (inputs) {
                         SDL_small_free(inputs, isstack);
                     }

src/video/windows/SDL_windowswindow.c

@@ -779,12 +779,12 @@ void WIN_GetWindowSizeInPixels(_THIS, SDL_Window *window, int *w, int *h)
     HWND hwnd = data->hwnd;
     RECT rect;
 
-    if (GetClientRect(hwnd, &rect)) {
+    if (GetClientRect(hwnd, &rect) && !IsRectEmpty(&rect)) {
         *w = rect.right;
         *h = rect.bottom;
     } else {
-        *w = 0;
-        *h = 0;
+        *w = window->w;
+        *h = window->h;
     }
 }