`text_err()` does:
```
len = vfprintf(stderr, format, ap);
pcmk__assert(len >= 0);
```
That shouldn't be an assertion, because it's reasonable for the caller of a command-line tool to have closed stderr (possibly because it died). Instead, we should just `crm_err()` the message if `vfprintf()` returns a negative result (which likely won't be seen either, but we might as well give some chance).
Reported seen in `pcmk__output_and_clear_error()` as a tool exits:
* [[https://issues.redhat.com/browse/RHEL-59043 | RHEL-59043]]