Error on project close if can_slave or can_master node was open

[Andrey Skvortsov]

Steps to reproduce:

1. Open canopen_master or canopen_slave example
2. Open can node in project tree
3. Double click on canopen slave/master node
4. Close project

Following traceback should happen:

Traceback (most recent call last):
  File "/home/developer/WorkData/PLC/beremiz/beremiz/BeremizIDE.py", line 935, in OnCloseProjectMenu
    self._Refresh(TITLE, EDITORTOOLBAR, FILEMENU, EDITMENU)
  File "/home/developer/WorkData/PLC/beremiz/beremiz/IDEFrame.py", line 917, in _Refresh
    self.RefreshFunctions[element]()
  File "/home/developer/WorkData/PLC/beremiz/beremiz/BeremizIDE.py", line 794, in RefreshEditMenu
    item = self.EditMenu.FindItemByPosition
  File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk3/wx/_core.py", line 12144, in FindItemByPosition
    return core.Menu_FindItemByPosition(*args, **kwargs)
PyAssertionError: C++ assertion "position < m_items.GetCount()" failed at ../src/common/menucmn.cpp(585) in FindItemByPosition(): wxMenu::FindItemByPosition(): invalid menu index