win32: Return 0 from WM_WINDOWPOSCHANGING if a resize is expected

This was accidentally removed while deleting some associated dead code.

src/video/windows/SDL_windowsevents.c

···
         break;
 #endif // WM_GETMINMAXINFO
 
+    case WM_WINDOWPOSCHANGING:
+
+        if (data->expected_resize) {
+            returnCode = 0;
+        }
+        break;
+
     case WM_WINDOWPOSCHANGED:
     {
         SDL_Window *win;