progress: avoid empty line when breaking the progress line

progress: avoid empty line when breaking the progress line

Since commit 545dc345eb (progress: break too long progress bar lines,
2019-04-12) when splitting a too long progress line, sometimes it
looks as if a superfluous empty line were added between the title
line and the counters.

To make sure that the previously displayed progress line is completely
covered up when writing the new, shorter title line, we calculate how
many characters need to be overwritten with spaces.  Alas, this
calculation doesn't account for the newline character at the end of
the new title line, and resulted in printing one more space than
strictly necessary.  This extra space character doesn't matter, if the
length of the previous progress line was shorter than the width of the
terminal.  However, if the previous line matched the terminal width,
then this extra space made the new line longer, effectively adding
that empty line after the title line.

Fix this off-by-one to avoid that spurious empty line.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>