Fix for installing parts to vehicle duplicating part

So, playing with my main file I realized that when you attempt to install a part to a vehicle from outside of your inventory, you have a chance to duplicate the installed item by attempting *again*, without moving, to install the part once more.

The issue occurs because the cache crafting_inv (of which the parts list to install is made from), does not update because the player has not moved. You'd figure since the turn was different...

So for now, just a minor fix so that while in a vehicle the cache is refreshed, disallowing duplication.

That's all!

-Davek

(P.S. I did a reset on the branch since I made some changes that broke map::unboard_vehicle (lol), so I reverted those and thus a million branch merge messages appeared! However the diff looks fine so I'm putting in this PR.)
I see, so there is a specific function for this. Let me make that change.

Also, it was more jargon for myself, flags to place true if the current character is crafting, but since there is an invalidate function, which looking now I TOTALLY overlooked, I can just use that instead.

Also, that was my statement, veh_at uses cache since it as accessed *everywhere* in this code base.