fix problem with SFC action/transition rename

Traceback (most recent call last):
File "/home/developer/WorkData/PLC/beremiz/beremiz/IDEFrame.py", line
1636, in OnProjectTreeItemEndEdit
elif new_name.upper() in [name.upper() for name in
self.Controler.GetProjectPouVariableNames(pou_name) if name !=
old_name]:
NameError: global name 'pou_name' is not defined