Fix "arriving at star"

[SpacialCircumstances]

Currently, when carriers arrive at an unclaimed star, the first carrier to arrive claims it. Because carriers are sorted by ship number and distance traveled, this works out fine.

However, we're just fixing #1341 where a star is conflicted to handle combat properly. To reallow star abandonment, the same fix needs to be applied to claiming unowned stars by rewriting the arrival logic.