dlm: never return invalid nodeid by dlm_our_nodeid()

This patch will remote the return of an invalid nodeid value when
local_comm is not set. This case should never happen as the DLM stack
tries to compare valid nodeids with an invalid nodeid returned by
dlm_our_nodeid(). Instead we let it crash to getting at least recognized
if we running into such state.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>