Fix: Code is actually reachable

[matthiasbeyer]

This fixes an reachable unreachable!() statement.
This might not be the approprite fix, although it resulted in no panic
in the code I used to test it, so it seems appropriate as a first idea
for a proper fix.

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If you think this is a good first idea, please release it as a patchlevel update (v0.16.1)!

Related to #285 (but there might be a better fix)

[mibac138]

Turns out is_hidden must return false for ProgressDrawTarget::Remote because otherwise progress bars won't notify the MultiProgress about their state changes thus deadlocking the program. However, a progress bars notifies a MultiProgress by (among others) sending it's drawn state and to draw this state width is required (for wide_bar and wide_message). MultiProgress just forwards fn width to draw_state.width which actually might be Hidden and actually reaching the 'unreachable' branch. I believe this is the simplest solution to this issue as otherwise we'd need to add a new mechanism that skips drawing when a progress bar's draw target is remote and that remote's target is hidden, which seems relatively complex compared to this one line fix.

MCVE:

use indicatif::{MultiProgress, ProgressDrawTarget, ProgressBar};

fn main() {
    let mpb = MultiProgress::with_draw_target(ProgressDrawTarget::hidden());
    let pb = mpb.add(ProgressBar::new(123));
    pb.finish();
    mpb.join().unwrap();
}

[djc]

I just published 0.16.1 which contains this fix (along with a few other ones).