Empty lines in `MultiProgress::println` leads to lost output about indicatif

[tgolsson]

I think my fix is maybe a bit too simplistic on the other edge now that I think about it, but if the location feels right I can do a robust solution with some proper tests.

[djc]

I don't remember all the context here, but it looks to me like real_len() is about the line width, not about the number of lines? @chris-laplante do you have an intuition for this?

[tgolsson]

As far as I can tell, it is the "sum of wrapped line count", i.e., number of lines once wrapping is applied.

[chris-laplante]

I don't remember all the context here, but it looks to me like real_len() is about the line width, not about the number of lines? @chris-laplante do you have an intuition for this?

I don't have this stored in my head anymore unfortunately :/. I will try to take some time over the coming holiday weeks to look at it.