_frontend/cli.py: Don't attempt to path NoneType in complete_target()
Description
In a situation where we were attempting auto-completion outside of a project directory (or a sub directory of) we were attempting to path against a non existent directory, internally trying to join to a NoneType. Before returning as with the case where we can't load a project.conf from yaml, return when we can't construct a path.
Changes proposed in this merge request:
- Return early before trying to load in a non existent yaml path for project.conf
This merge request, when approved, will close: #958 (closed)