Check for arrivals after setting expedition position

I ran into an issue where any time a page was loaded scrolled to a position other than the top, the following sequence would occur:

1. `set_expedition_position()` was called initially on line 31
2. the `scroll.fndtn.magellan` event triggered `check_for_arrivals()`
3. the `resize.fndtn.magellan` event triggered `set_expedition_position()` again

Because the scroll occurred before the resize, `check_for_arrivals()` (and therefore `update_expedition_positions()`) was never called again and my nav bar would disappear off screen.

I've added `check_for_arrivals()` to the end of `set_expedition_position()`, since it's currently not guaranteed to be called otherwise.