Escaping problem when saving to a new file

Steps to reproduce:

• Create a new project, add a title clip
• Save, enter name "Untitled %00.xges", notice backtrace:

Traceback (most recent call last):
  File "/home/aleb/dev/pitivi/pitivi/pitivi/editorperspective.py", line 407, in __save_project_as_cb
    self.saveProjectAs()
  File "/home/aleb/dev/pitivi/pitivi/pitivi/editorperspective.py", line 728, in saveProjectAs
    x = self.app.project_manager.saveProject(uri)
  File "/home/aleb/dev/pitivi/pitivi/pitivi/project.py", line 372, in saveProject
    uri = quote_uri(uri)
  File "/home/aleb/dev/pitivi/pitivi/pitivi/utils/misc.py", line 185, in quote_uri
    return Gst.filename_to_uri(raw_path)
ValueError: embedded null byte

First task would be to add a unittest.