Ensure that wnd is not None before calling Hide

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@45874 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

wxPython/wx/lib/customtreectrl.py

@@ -3562,6 +3562,7 @@ class CustomTreeCtrl(wx.PyScrolledWindow):
         for child in self._itemWithWindow:
             if not self.IsVisible(child):
                 wnd = child.GetWindow()
+                if wnd:
                     wnd.Hide()