user32: Try to activate topmost activable window in WINPOS_ActivateOtherWindow.

dlls/user32/tests/win.c

@@ -3766,6 +3766,11 @@ static void test_SetParent(void)
     ok(bret, "SetForegroundWindow() failed\n");
     check_active_state(popup, popup, popup);
 
+    ShowWindow(parent, SW_SHOW);
+    SetActiveWindow(popup);
+    ok(DestroyWindow(popup), "DestroyWindow() failed\n");
+    check_active_state(parent, parent, parent);
+
     ok(DestroyWindow(parent), "DestroyWindow() failed\n");
 
     ok(!IsWindow(parent), "parent still exists\n");

dlls/user32/winpos.c

@@ -1536,7 +1536,19 @@ void WINPOS_ActivateOtherWindow(HWND hwnd)
     for (;;)
     {
         if (!(hwndTo = GetWindow( hwndTo, GW_HWNDNEXT ))) break;
-        if (can_activate_window( hwndTo )) break;
+        if (can_activate_window( hwndTo )) goto done;
+    }
+
+    hwndTo = GetTopWindow( 0 );
+    for (;;)
+    {
+        if (hwndTo == hwnd)
+        {
+            hwndTo = 0;
+            break;
+        }
+        if (can_activate_window( hwndTo )) goto done;
+        if (!(hwndTo = GetWindow( hwndTo, GW_HWNDNEXT ))) break;
     }
 
  done: