Add: basic sanity check for 'articulated_part' callback

[glx22]

When an item has an articulated_part callback, it's quite common to use this item as result of the callback.

It's also quite common to forget IDs for articulated_part results must be in 0 .. 16383 range.

Detect the possible mistake, and warn users about it.

[andythenorth]

Confirmed working as intended.