D10315 is going to make egrep_empty_invalid an actually invalid regex,
to be consistent with the equivalent BRE "{" behavior, when using regex(3).
This test case is ultimately testing for the wrong thing- we're trying to detect
a clean exit, which can be pretty much any non-0 exit value depending on how the
installed grep interprets the expression. gnugrep interprets it as non-matching,
and in the future bsdgrep will interpret it is an error.
Ultimately, we don't care if grep exits with 1 or > 1 since interpretation is
implementation defined, so we use not-exit:0 instead to respect this.
While here, make sure bsdgrep isn't leaking regex(3) errors with the -q flag, also
detected following D10315.