fix bug that appears if datatype in the project tree is renamed to wrong name (keyword, existend type,...)

Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk2/wx/_core.py", line 16765, in <lambda>
lambda event: event.callable(*event.args, **event.kw) )
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk2/wx/lib/expando.py", line 126, in _adjustCtrl
numLines = self.GetNumberOfLines()
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk2/wx/_core.py", line 16710, in __getattr__
raise PyDeadObjectError(self.attrStr % self._name)
PyDeadObjectError: The C++ part of the TreeTextCtrl object has been deleted, attribute access no longer allowed.

<?xml version='1.0' encoding='utf-8'?>
<PyFile xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <variables>
    <variable name="SomeVarName" type="DINT"/>
    <variable name="Grumpf" type="STRING"/>
  </variables>
  <globals>
    <xhtml:p><![CDATA[
print "All python PLC globals variables :", PLCGlobalsDesc
print "Current extention name :", __ext_name__
]]></xhtml:p>
  </globals>
  <init>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </init>
  <cleanup>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </cleanup>
  <start>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </start>
  <stop>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </stop>
</PyFile>