Allow People to re-enter the arrivals shuttle

[Roomba]

The general arrivals area tends to get fucked over more in Cog2 than previous maps due to it being less isolated. But yes, antags will 100% camp/otherwise render the arrivals shuttle uninhabitable. I've been immediately fireballed and assaulted by golems upon spawning on several occasions, and recently there was a round where a mechanic set up cloaked crushers in the shuttle when no admins were on. (Largely because of that fact, no doubt. Yes this was adminhelped multiple times over the course of the round, to no avail.)

I dunno if much can be done about blobs, any blob spawning in that quadrant kind of has to take over most of arrivals by nature. Expanding directly onto the shuttle is definitely a crappy move, though.