UI_MainMap.VesselChange is expensive during RUD

[JonnyOThan]

This fires for every part destruction / joint break event. There are a lot of those in a single frame when crashing a large ship into the ground. Can fix this 2 ways (likely both):

1. Instead of taking immediate action, set a flag and then handle it in LateUpdate so that it happens once per frame instead of once per part
2. Be smarter about checking whether anything actually needs to be updated