Fixed missing resolve-case for Allocation promise
Fixed missing resolve-case for Allocation promise

There was a case when a project-less instances w/ allocation source set
could be missed altogether. The promise-chain for USE_ALLOCATION_SOURCE
had an edge-case where `resolve()` was *not* called and denied the
follow-up `then()`s then being able to handle the situation.

To re-produce this, set USE_ALLOCATION_SOURCE = True and then remove
the project from an existing instance with "allocation_source":

```python
from core.models import ProjectInstance
pi = ProjectInstance.objects.get(
   instance__provider_alias="82a2d6fb-f079-4ca9-85ad-806eb88da563")
pi
pi.delete()
```

note: example above from `./manage.py shell` REPL session

CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend