remaining_len - 1 may result in "attempt to subtract with overflow"

[grovesNL]

It's possible that remaining_len attempts to subtract 1 from 0 in certain cases (I ran into it when testing font sizes in my application).

cosmic-text/src/buffer.rs

Line 241 in 9a4d067

self.remaining_len -= 1;

I think it might happen when the layout line can't into the dimensions or something similar. I'll work on simplifying my test case down to verify but wanted to create this issue so I don't forget about it.

[grovesNL]

It seems to be something about being right at the edge of a line, here's a repro using the rich-text example (unchanged) from main:

[grovesNL]

As the font size and line height increases it becomes more likely to hit this (reason described in #82), which is why I noticed this while I was increasing my font size.