Description of bug:

I know there are open bug(s) about toolchange customization, but this one should be easy to consider out of step.

I'm using LinuxCNC and T0 specifically means 'no tool', aka 'unload tool, leave spindle empty'. pcb2gcode really needs to start indexing at 1 in the default case.

Anecdotally I've been told that many other machines take the same meaning, though I can't cite reference for them:

https://linuxcnc.org/docs/html/gcode/other-code.html#sec:select-tool specifically the first note in this section.