Items table crafting fixing

* Fixes #4820 

For recipes containing _/obj/items_ (meteorshell and pulseshell are, currently, the only recipes containing these), the problem was that, when looking for _n_ items of the same type in the table content, it located _n_ times the same one.

When a corresponding item is found in the table content, it's location is now set to _null_ to prevent that (the item is eventually relocated into the newly craft item further in the code).

Note that meteorshell is supposed to requires two manipulators, as pulseshell is supposed to requires two advanced capacitors.

* Small typo in construction fixed