Fix removing inclusive filters in getCollection

[newbthenewbd]

In Grav 1.6.31, a collection like this:

items:
  - '@root.descendants'
filter:
  published: true
  non-published: true

...catches all pages, published or not. This is thanks to the removal of inclusive sets before they are parsed.

It seems that sometime during the refactoring done in Grav 1.7, this removal of inclusive sets had gone missing. As a result, a collection like above first filters out non-published pages, then the published ones, and ends up empty. This pull request aims to fix that.

Bottom line, I think that this issue deserves a fairly high-priority fixing, as I'd imagine that this isn't the only workflow around that it is capable of breaking...

Thank You!

[mahagr]

The new filters work as: published: true (all published), published: false (all unpublished), and published: null (ignore state).

So basically I wanted to get rid of the non- versions of the variables as they needlessly complicate the logic. I will accept the fix as I didn't mean to break existing behavior, but I will need to update it to work with the false value.