Fix wxFindWindowAtPoint() with nested windows in wxMSW.

Return the deepest child of the window and not the first one as this function
needs to return the window that is at the top of Z-order.

Closes #14591.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72470 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/window.cpp

@@ -7215,9 +7215,21 @@ wxWindow* wxFindWindowAtPoint(const wxPoint& pt)
     {
         // WindowFromPoint() ignores the disabled children but we're supposed
         // to take them into account, so check if we have a child at this
-        // coordinate.
-        ::ScreenToClient(hWnd, &pt2);
-        hWnd = ::ChildWindowFromPointEx(hWnd, pt2, CWP_SKIPINVISIBLE);
+        // coordinate using ChildWindowFromPointEx().
+        for ( ;; )
+        {
+            pt2.x = pt.x;
+            pt2.y = pt.y;
+            ::ScreenToClient(hWnd, &pt2);
+            HWND child = ::ChildWindowFromPointEx(hWnd, pt2, CWP_SKIPINVISIBLE);
+            if ( child == hWnd || !child )
+                break;
+
+            // ChildWindowFromPointEx() only examines the immediate children
+            // but we want to get the deepest (top in Z-order) one, so continue
+            // iterating for as long as it finds anything.
+            hWnd = child;
+        }
     }
 
     return wxGetWindowFromHWND((WXHWND)hWnd);