Fix end of progress bar

[christiangnrd]

The progress bar would "bounce" by not printing any :light_black characters when n_left == 0 but n_filled != max_progress_width.

#Before
julia> bar.current=980;show_progress(stdout,bar)
 Downloading packages ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╺ 980/1000
#After
julia> bar.current=980;show_progress(stdout,bar)
 Downloading packages ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 980/1000