pgsql: Fix \watch's interaction with libedit on ^C.

Fix \watch's interaction with libedit on ^C.

When you hit ^C, the terminal driver in Unix-like systems echoes "^C" as
well as sending an interrupt signal (depending on stty settings). At
least libedit (but maybe also libreadline) is then confused about the
current cursor location, and corrupts the display if you try to scroll
back. Fix, by moving to a new line before the next prompt is displayed.

Back-patch to all supported released.

Author: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Reported-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/3278793.1626198638%40sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/21267b64771925c154a767b1f261b5501d7bb26f

Modified Files
--------------
src/bin/psql/command.c | 12 ++++++++++++
1 file changed, 12 insertions(+)