Revert Model coalesce

[MGatner]

Description
The following change was made to Model::__get() to simplify code with null coalescence: ace9df0#diff-1a690370bdbdc5997068f9ff210bacef314eeb65d1df73af206783ce055d8d1d

However, because of the magic accessors on BaseModel and Connection this did not end up being logically equivalent. Reverting that part of the PR.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• n/a User guide updated
• Conforms to style guide

[paulbalandan]

Hmm.. So my hunch before was right that it doesn't sit right.

[MGatner]

Yep. I'm not actually ever sure what is happening but Model is causing calls to Connection that it never used to. I think we need to leave these things alone, and in version 5 have a rule for "no magic calls/access to classes with magic". It's too messy.