Fix: A positive inset was also shortening the whole key

[nharrer]

Fix for #175

The bug was introduced in commit e88a398, which allowed the stem to stick out of the key (negative inset). However it broke positive insets (recessed stem).

[dsz-dsz-k]

Hi !
I'm glad I stumbled on your solution because I was at a loss trying to fix the inset function.
I've got another problem (see this issue: #203), would you happen to have some hint about it?

Thanks for your help.