Potential issue with asynchronous shuttle loading causing half of shuttles to be deleted

[PowerfulBacon]

I found an issue on a local fork during testing that some weird behaviour can occur when calling initiate docking outside of the shuttle subsystem. initiate_docking can sleep, which means the shuttle subsystem can run while initiate docking is in the process of happening. This means that in rare occassions, the transit port attached to a shuttle can be deleted while it is halfway through docking with the other shuttle. When this occurs, non deterministic behaviour arrises which either:

• Fully deletes the shuttle (The shuttle seems to be outside of the transit zone for some reason?)
• Half of the shuttle gets deleted (I have no idea why this happens, in theory the shuttle should be fully contained with in the dock)
• Doesn't delete the shuttle at all (SSshuttle transit reset doens't fire during docking, or CHECK_TICK doesnt fire)

[PowerfulBacon]

I should mention that I fixed this by creating a new variable on the mobile port called is_moving, and if the port is moving don't allow its transit port to be cleared. This fixed the issue.