fix: save the workzero if set manually

[blaggacao]

Expected

1. User sets workzero
2. Either: a) reset occurs or b) a M0
3. The workzero remains set

Actual (before this patch)

1. User sets workzero
2. Either: a) reset occurs or b) a M0
3. The workzero is reset to something else (what had been stored inside config-override.g)

[blaggacao]

@chrishamm Would you kindly consider this (or a similar) improvement to the UI?

[blaggacao]

@chrishamm This now targets v3.7-dev as requested in the forum.

[chrishamm]

I'm not sure if this is right, no other buttons in DWC call M500 because not everyone uses config-override.g. I'd be happy to make that change if there is a new option in the machine settings to specifiy if M500 may be called on workzero changes, though.