Account for raw limits properly in CalendarEventQuery

Summary:
Fixes T8613. This was pretty straightforward, I just never dug into it originally.

rawResultLimit = 0 just means "no limit", so the fix is to only apply a limit if it is set to some nonzero value.

Also modernize a few pieces of code.

Test Plan: I'm actually not sure this can actually be hit normally? I faked setGenerateGhosts(true) into an unrelated query, hit the fatal, then fixed it.

Reviewers: lpriestley, chad

Reviewed By: chad

Maniphest Tasks: T8613

Differential Revision: https://secure.phabricator.com/D15653