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.stehule@gmail.com>
Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/3278793.1626198638%40sss.pgh.pa.us

Branch
------
REL_10_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/7c5953b7b5dc2b1c5546c5b8b8b29785d46f4e8e

Modified Files
--------------
src/bin/psql/command.c | 8 ++++++++
1 file changed, 8 insertions(+)