Fix divide by zero exception in InterlockingGenerator.

[mpaperno]

Fixes #9910

There's a more fundamental issue in that the current config option minimum/maximum value types are int, so setting a minimum of something like 0.1 doesn't work (minimum becomes zero). The GUI validation then doesn't work as expected. Some of the code seems to completely ignore that fact, like for this interlocking beam width option:

BambuStudio/src/libslic3r/PrintConfig.cpp

Line 3379 in 6a3e8bb

def->min = 0.01;

I'll likely submit a PR for that fix next, unless it turns into a bigger deal than it appears so far.

Thanks,
-Max

[mpaperno]

Somewhat related:

The generator hangs during slicing when the beam width gets "too small". I'm not clear on what defines the actual practical lower limit. For example on an arbitrary test object (some text on bottom of a cube), using .4 nozzle with .2 layer height and .42 line width, reducing the beam width to 0.1 caused a hang. With 0.2 width it took a long time but completed (though generated "garbage"). After switching to .6 nozzle w/ .3/.62 height/width, it no longer hangs with a beam width of 0.1, but will with 0.01 (the currently configured minimum value).

@Noisyfox Perhaps you can take a look? (I think you originally ported this? If not, sorry and NVM!) It's probably preferable not to impose some arbitrary minimum, if it could be calculated. Or maybe the algorithm could be improved to skip unworkable cells?

There's no way to exit gracefully after a hang, the "stop" button in the status bar window is ineffective. Which is likely a separate issue in general (haven't looked).

-Max