Fix unfolded vehicles not driveable before stepping off/on

[irwiss]

Summary

Bugfixes "Fix unfolded vehicles not driveable before stepping off/on the tile"

Purpose of change

Fixes #54026

Describe the solution

Both unfolds (the new generic vehicle and the old convertible one) were skipping over map::board_vehicle so player's in_vehicle = false prevented driving when pressing ^ before stepping out of/into the controls tile.

Also one was missing adding vehicle to cache and the other had a weird nullcheck after already dereferencing so I rearranged the calls a bit to make them cohesive and more or less the same.

Had to go on a hunt into tests why it was complaining about unboarding; vehicle hp with degradation tests read a bit weird, can't see where they clean up the created vehicles, may be I missed it somewhere, but unboarding at end of check is enough to pass tests.

Also changed debugmsg when boarding to make it clear what was missing ( in one case it was a non-broken boardable part )

Describe alternatives you've considered

Testing

Spawn folding bicycle, unfold, press ^ - just the controls screen pops up (this is the convertible unfold)
Spawn wheelchair do the same (this is using generic unfold)
Apply patch
Do the above again and you should be able to drive immediately after unfolding

Additional context