Prevent a close(0) in free_muxlist().

Fixes sy{mux,mon} reconfiguration w/ SIGHUP.

Confirmed by Willem Dijkstra, OK henning@

sysutils/symon/patches/patch-lib_data_c

@@ -0,0 +1,16 @@
+$OpenBSD: patch-lib_data_c,v 1.1 2007/06/20 17:11:34 mpf Exp $
+--- lib/data.c.orig	Wed Jun 20 09:57:02 2007
++++ lib/data.c	Wed Jun 20 09:58:46 2007
+@@ -862,8 +862,10 @@ free_muxlist(struct muxlist * mul)
+         if (p->port != NULL)
+             xfree(p->port);
+ 
+-        close(p->clientsocket);
+-        close(p->symuxsocket);
++        if (p->clientsocket)
++            close(p->clientsocket);
++        if (p->symuxsocket)
++            close(p->symuxsocket);
+         for (i = 0; i < AF_MAX; i++)
+             if (p->symonsocket[i])
+                 close(p->symonsocket[i]);