Fix rare problem allocating frec for DNSSEC.

A call to get_new_frec() for a DNSSEC query could manage to
free the original frec that we're doing the DNSSEC query to validate.
Bad things then happen.

This requires that the original frec is old, so it doesn't happen
in practice. I found it when running under gdb, and there have been
reports of SEGV associated with large system-clock warps which are
probably the same thing.

src/dnsmasq.c

@@ -1683,7 +1683,7 @@ static int set_dns_listeners(time_t now)
   
   /* will we be able to get memory? */
   if (daemon->port != 0)
-    get_new_frec(now, &wait, 0);
+    get_new_frec(now, &wait, NULL);
   
   for (serverfdp = daemon->sfds; serverfdp; serverfdp = serverfdp->next)
     poll_listen(serverfdp->fd, POLLIN);