Comment 2 for bug 669479

Steps to reproduce:
1. Create a task 'Lunch'
2. Create a subtask for it called '@buy Milk'
3. Open and close an editor of 'Lunch' task few times

After a while the task editor can't be opened and there is a traceback in terminal:

Traceback (most recent call last):
  File "/home/izidor/projekte/gtg/gtg/GTG/gtk/editor/taskviewserial.py", line 159, in unserialize
    success = self.parsexml(content_buf, ite, element.firstChild)
  File "/home/izidor/projekte/gtg/gtg/GTG/gtk/editor/taskviewserial.py", line 208, in parsexml
    text = n.firstChild.nodeValue
AttributeError: 'NoneType' object has no attribute 'nodeValue'
Traceback (most recent call last):
  File "/home/izidor/projekte/gtg/gtg/GTG/gtk/browser/browser.py", line 1041, in on_edit_active_task
    self.vmanager.open_task(tid)
  File "/home/izidor/projekte/gtg/gtg/GTG/gtk/manager.py", line 177, in open_task
    clipboard = self.clipboard)
  File "/home/izidor/projekte/gtg/gtg/GTG/gtk/editor/editor.py", line 130, in __init__
    self.textview.insert("%s"%texte)
  File "/home/izidor/projekte/gtg/gtg/GTG/gtk/editor/taskview.py", line 269, in insert
    self.buff.deserialize(self.buff, self.mime_type, _iter, text)
glib.GError: Unknown error when trying to deserialize application/x-gtg-task