Fixes multiple airlocks on same tile

Fixes #5809

* Added check for RCD and manual airlock assembly wrenching for airlock on tile already
* Added use of "working" var to stop spam clicking with RCD airlock creation
It stops multiple airlocks being built at once. You have to wait for the "do_after" to build another, now. "working" is declared before this PR was made, not sure what its original use was but it's not used anywhere.