fix Traceback if search icon on library panel is clicked, when no
category/item is selected in the library.

The problem is here, that if nothing is selected method GetSelection()
returns root item, that doesn't have any python data associated with it.
This issue seems to be wx3.0 specified, because it doesn't exist
with wx2.8 on Windows.

from py_ext import *
from PythonEditor import PythonEditor
from PythonFileCTNMixin import PythonFileCTNMixin