wxGUI/modeler: fix handling error when unable to open input model file

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@67286 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gmodeler/model.py

@@ -296,7 +296,7 @@ class Model(object):
         try:
             gxmXml = ProcessModelFile(etree.parse(filename))
         except StandardError as e:
-            raise GException(e)
+            raise GException(unicode(e))
         
         if self.canvas:
             win = self.canvas.parent