fix: initialize next_box_height to avoid unboundlocalerrors

[filipweidemann]

As promised in #2106, this is my proposed fix for UnboundLocalErrors inside of the layout/column.py module.

I am still not sure yet if initializing the value with 0 is the right move here, however, in our case, monkey-patching it this way seemed to work without any further problems.

Let me know if this is fine.

[FelixSchwarz]

I basically know next to nothing about the WeasyPrint code but the change looks good to me.

[liZe]

I basically know next to nothing about the WeasyPrint code but the change looks good to me.

It looks good to me too, but I’d like to have a way to reproduce the problem before merging, so that we can add a test. See #2106.

[liZe]

Closing, as we didn’t find a way to reproduce this bug. If it happens again, it may come from another error somewhere else that we don’t want to let pass silently.