fix(gx): correct stub handler for WM_SIZING in d3d backend

src/gx/d3d/CGxDeviceD3d.cpp

@@ -350,7 +350,7 @@ LRESULT CGxDeviceD3d::WindowProcD3d(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM
     case WM_SIZING: {
         // TODO
 
-        break;
+        return 1;
     }
 
     default: