start-stop-daemon: don't fail stopping if pidfile is gone

If pidfile does not exist when we are stopping the daemon, assume it is
already stopped, and report success.

hostapd is an example of a daemon which removes its pidfile when it is
exiting. If this daemon terminates prematurely, that is, without s-s-d
involvement, then openrc fails to restart it, because s-s-d "stop"
command fails when pidfile is missing.

X-Gentoo-Bug: 646274
X-Gentoo-Bug-URL: https://bugs.gentoo.org/646274

src/rc/start-stop-daemon.c

@@ -661,7 +661,7 @@ int main(int argc, char **argv)
 			parse_schedule(applet, NULL, sig);
 		if (pidfile) {
 			pid = get_pid(applet, pidfile);
-			if (pid == -1)
+			if (pid == -1 && errno != ENOENT)
 				exit(EXIT_FAILURE);
 		} else {
 			pid = 0;