Don't stumble over zero pid fields.

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4546 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/shmlog.c

@@ -336,7 +336,7 @@ vsl_goodold(int fd)
 	if (slh.start != sizeof slh + sizeof *params)
 		return (0);
 
-	if (!kill(slh.master_pid, 0)) {
+	if (slh.master_pid != 0 && !kill(slh.master_pid, 0)) {
 		fprintf(stderr,
 		    "SHMFILE owned by running varnishd master (pid=%jd)\n",
 		    (intmax_t)slh.master_pid);