bug#46609: Fix shell password prompt in minibuffer (bug 43302)

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Ryan Prior <rprior@protonmail.com>,  46609@debbugs.gnu.org
> Date: Thu, 18 Feb 2021 15:47:39 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> I am not a Unicode expert and don't know if there might be undesirable
> >> side-effects from using :space: instead of :blank:. However, in my
> >> manual testing these change give me the exact behavior I'm after.
> >
> > I'm a bit worried by the [[:space:]]* part: it would match any number
> > of newlines and ^L characters, right?  Is that what we want here?
> 
> I think so -- matching "Password: \n\n" makes as much sense as matching
> "Password: \n", I think?

It actually happens in Real Life?

What bothers me is that we could takes something unrelated as a
password prompt.