status: make coloring of "-z --short" consistent

When running "git status -z --short", the marker on modified index
entries (e.g., "M") is colorized, but the "??" marker for untracked
entries is not. Let's fix the "??" entries to show color here.

At first glance you might think that neither should be colorized, as
usually one would use "-z" to get machine-readable output. But this is a
tricky and unusual case. We have two output formats, "--short" and
"--porcelain" which are substantially similar, but differ in that
"--short" is for humans who want something short and "--porcelain" is
for machines. And "-z" by itself, without any other output option, does
default to "--porcelain", so "git status -z" will not colorize anything.

But if you explicitly ask for "-z" and "--short" together, then that is
asking for the human-readable output, but separated by NULs. This is
unlikely to be useful directly, but could for example be used if the
output will be shown to a human outside of the terminal. At any rate,
the current behavior is clearly wrong (since we colorize some things but
not others), and I think colorizing everything is the least-surprising
thing we can do here.

Reported-by: Langbart <Langbart@protonmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>