When the _RC_RUNFILE (by some ill chance) happened to be empty or

reading it failed, ${pexp} ended up as the empty string and the script
would send SIGTERM to init(1), which was really inconvenient.
Fix that by never allowing pexp to become empty.
My patch considerably simplified by and ok  ajacoutot@.

src/etc/rc.d/rc.subr

@@ -1,4 +1,4 @@
-#	$OpenBSD: rc.subr,v 1.52 2011/10/09 08:48:53 ajacoutot Exp $
+#	$OpenBSD: rc.subr,v 1.53 2011/10/09 16:46:55 schwarze Exp $
 #
 # Copyright (c) 2010, 2011 Antoine Jacoutot <ajacoutot@openbsd.org>
 # Copyright (c) 2010, 2011 Ingo Schwarze <schwarze@openbsd.org>
@@ -34,7 +34,8 @@ rc_write_runfile() {
 }
 
 rc_read_runfile() {
-	[ -f ${_RC_RUNFILE} ] && pexp=$(< ${_RC_RUNFILE})
+	[ -f ${_RC_RUNFILE} ] && local _new_pexp=$(< ${_RC_RUNFILE})
+	[ -n "${_new_pexp}" ] && pexp="${_new_pexp}"
 }
 
 rc_rm_runfile() {