wxGUI: GetMenuCmd - initialize cmd variable

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@53447 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/lmgr/frame.py

@@ -574,6 +574,8 @@ class GMFrame(wx.Frame):
         
         if event:
             cmd = self.menucmd[event.GetId()]
+        else:
+            cmd = ''
         
         try:
             cmdlist = cmd.split(' ')