Fix issue introduced in f2afca0f437c211d87b05e8e59d632fa3bd2c5fc: with single bin in Z, field was always returned instead of obeying the thickness domain
Fix issue introduced in f2afca0f437c211d87b05e8e59d632fa3bd2c5fc: with single bin in Z, field was
always returned instead of obeying the thickness domain

Koensw/allpix-squared,Koensw/allpix-squared,Koensw/allpix-squared,Koensw/allpix-squared