[FR] Try not to crash the printer by writing bad values

[ali1234]

Describe the new feature or functionality, and how it should work When editing the mesh, if you put an invalid Z value (ie one which is not a multiple of 0.025) or simply leave the Z field blank, the printer returns a M421 incorrect parameter error, and then Octoprint shuts it down with M112, requiring a power cycle. This is annoying.

Instead, the plugin should refuse to send these incorrect values, especially if the Z value field is completely blank.

Firmware Marlin 2.1.2.3 - self-compiled.