Allow for using 0 for the Normal step in the Exposure time finder

[Pauan]

I'm trying to use the "Multiple exposures" feature to calibrate the optimal bottom exposure time for my printer.

However, it does not allow me to enter 0 into the "Normal step" field. It is clamped at a minimum of 0.01.

This means that it will increment the normal exposure on each test... I don't want that.

I only want to increment the bottom exposure, not the normal exposure.

This can be fixed by simply allowing users to use 0 for the "Normal step".

[sn4k3]

Last release fix that.

[Pauan]

I have confirmed that it is working in the latest version. Thank you so much!