Don't check children of minimized windows in get_update_region.

diff --git a/server/window.c b/server/window.c
index 88dfe8f..5143808 100644
--- a/server/window.c
+++ b/server/window.c
@@ -1627,7 +1627,8 @@
     {
         /* if window doesn't need any repaint, check the children */
         if (!(flags & UPDATE_NOCHILDREN) &&
-            ((flags & UPDATE_ALLCHILDREN) || (win->style & WS_CLIPCHILDREN)))
+            ((flags & UPDATE_ALLCHILDREN) || (win->style & WS_CLIPCHILDREN)) &&
+            !(win->style & WS_MINIMIZE))
         {
             reply->flags = get_child_update_flags( win, flags, &win );
         }