Account for raw limits properly in CalendarEventQuery
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