Only measure child rectangles of visible children when deciding about
scroll bars.

diff --git a/windows/mdi.c b/windows/mdi.c
index 9f4bddb..07cd19c 100644
--- a/windows/mdi.c
+++ b/windows/mdi.c
@@ -2243,7 +2243,8 @@
               WIN_ReleaseWndPtr(Wnd);
 	      return;
 	  }
-	  UnionRect( &childRect, &pWnd->rectWindow, &childRect );
+          if( pWnd->dwStyle & WS_VISIBLE )
+              UnionRect( &childRect, &pWnd->rectWindow, &childRect );
     } 
     WIN_ReleaseWndPtr(pWnd);
     UnionRect( &childRect, &clientRect, &childRect );