fix terminal resize crash

[nick1udwig]

Problem

resolves #806

Solution

Don't allow overflow/underflow

Testing

Try making terminal "too small"

Docs Update

None

Notes

None

[0x70b1a5]

still happens

thread 'main' panicked at hyperdrive/src/terminal/mod.rs:74:17:
           attempt to subtract with overflow
           note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

just run in cursor terminal and click the split terminal button until you have a bunch open

[nick1udwig]

Aha, getting closer: that's a different line. I've replaced all of those similar subtractions with saturating_subs; seems to work now: