wxGUI: try to import wx.lib.agw.customtreectrl first (see https://trac.osgeo.org/grass/changeset/41218)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@41219 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gui_modules/help.py

@@ -22,7 +22,10 @@ for details.
 import os
 
 import wx
-import wx.lib.agw.customtreectrl as CT
+try:
+    import wx.lib.agw.customtreectrl as CT
+except ImportError:
+    import wx.lib.customtreectrl as CT
 import wx.lib.flatnotebook as FN
 import  wx.lib.scrolledpanel as scrolled
 from wx.lib.wordwrap import wordwrap