minor: moving to 0,0 after setting 0,0 cause a slight movement

[stefanix]

Cheewee says: "One thing i noticed is when you click on the cutting area to set 0,0, when you then push 0,0 to go to the origin, the gantry moves a little. I suspect it's because of floats vs ints, but I couldn't figure out where the difference was in the code."