[BUGFIX][MER-2570] Fix error accessing project preview

[simonchoxx]

MER-2570

Fixed a couple of bugs when rendering the project preview.

• Error when calling DeliveryResolver instead of calling AuthoringResolver. This was failing when you have one selection criteria for an activity bank by objective and there is no objective added in the activity banks.

• Error when applying a selection criteria by item type and there is no such activity in the activity bank.

[gastonabella]

I'm not sure if I'm understanding this change. The DeliveryResolver function expects a section slug while the AuthoringResolver one expects a project slug, so why are we switching functions here?

[darrensiegel]

This selection renderer is unique - as it only ever gets called during page preview. In normal delivery, by the time we get to rendering the activity bank selections have been "fulfilled" and have been replaced by actual activities. For page preview, we do not fulfill bank selections, we instead leave them in the page model and this rendering code provides a summary of them to the author. So that being said, we never want to use the DeliveryResolver in this code, we only want to resolve to the Authoring revisions.

I suspect the use of DeliveryResolver was the problem and what was yielding the nil ids. I think we should simplify this code to:

 Oli.Publishing.AuthoringResolver.from_resource_id(section_slug, ids). # This section_slug really is the project slug
|> Enum.filter(fn r -> !is_nil(r) end)
|> Enum.reduce(%{}, fn rev, m -> Map.put(m, rev.resource_id, rev.title) end)