assert,tty: fix indicator and warning

Please have a look at the commit messages. I can split this into two PRs but I stumbled upon both things at the same time and they seemed small enough that individual commits might suffice.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines