service: do not let a script timeout take PID 1 with it

A stop: or reload: script written with a timeout killed Finit at
config load:

    service stop:5,/bin/true service.sh -- Boom

parse_script() takes the timeout as a pointer and the caller decides
whether it wants one.  However, both stop: and reload: scripts so far
have no timeout, i.e., NULL.  Guard the branch that reads a leading
number.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/service.c

@@ -1654,7 +1654,8 @@ static void parse_script(svc_t *svc, char *type, char *script, int *tmo, char *b
 			     script, errstr);
 			goto err;
 		}
-		*tmo = (int)(sec * 1000);
+		if (tmo)
+			*tmo = (int)(sec * 1000);
 	} else {
 		path = script;
 		if (tmo)