Segfault when adding clip to group

Submitted by Alexandru Balut `@aleb`

Link to original bug (#793882)

Description

Run the script below, notice the segfault:

from gi.repository import Gst  
Gst.init(None)  
  
from gi.repository import GES  
GES.init()  
  
group = GES.Group()  
clip = GES.TitleClip()  
group.add(clip)

.. because the clip has not been added to a layer.

It should not segfault.