`pgrep -x somecommand` exits with a non-zero status if it finds no
process running with the given name. When using home-manager as a
NixOS module, on boot (when sway isn't running) this script would
fail and then fail the unit since it seems the onChange scripts
are running with the -e switch.
This change ensures we're always returning a 0 exit status where we
attempt to get the pid of sway - we're only interested in either the
pid or an empty string, the exit status isn't important.
8a160f01ab