wxGUI: fix variable initialization

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@41621 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gui_modules/gmodeler.py

@@ -117,6 +117,7 @@ class ModelFrame(wx.Frame):
 
     def OnModelOpen(self, event):
         """!Load model from file"""
+        filename = ''
         global debug
         if debug is False:
             dlg = wx.FileDialog(parent = self, message=_("Choose model file"),