Fix PR remote/15974

In remote-notif.c:handle_notification, we have a loop,

  for (i = 0; i < ARRAY_SIZE (notifs); i++)
    {
      nc = notifs[i];
      if (strncmp (buf, nc->name, strlen (nc->name)) == 0
	  && buf[strlen (nc->name)] == ':')
	break;
    }

  /* We ignore notifications we don't recognize, for compatibility
     with newer stubs.  */
  if (nc == NULL)
    return;

If the notification is not in the list 'notifs', the last entry is
used, which is wrong.  It should be NULL.  This patch fixes it.

gdb:

2013-12-02  Pedro Alves  <palves@redhat.com>

	PR remote/15974
	* remote-notif.c (handle_notification): Return early if no
	notification is found.