Grilo Media item's composer is set to None which causes a TypeError
Submitted by Sambhav Kothari
Link to original bug (#775899)
Description
Grilo media item's composer is get in _add_search_item() in searchview which is sometimes returned none.
This is then directly set without validation which causes a TypeError when set_composer() is called on _albums[key].
To rectify the above a new getter was added to utils.py similar to artist and album getter.
This also completes one of the To-Dos in search which was required to properly render treeview as it doesn't accept none objects.