Skip showing 'no results' if find bar is already closed.

For #2568.

The issue is that with my latest changes, the module-global `modalBar` var actually gets nulled out when it's closed (whereas before, it was just a closure variable that got passed around and never nulled). I think nulling it out is proper behavior, so I just put a guard around the one place that could refer to the modalBar after it had been closed (in `findFirst()`)--it's okay to do nothing in that case since all it was doing was reddening the text field in the modalBar to show "no results".

Additionally, I removed the `modalBar` argument from all the functions that had been passing it around, since it's now a module global. (Should have done this in the previous pull.)