fs: dlm: fix missing pending to false

This patch sets the process_dlm_messages_pending boolean to false when
there was no message to process. It is a case which should not happen
but if we are prepared to recover from this situation by setting pending
boolean to false.

Cc: stable@vger.kernel.org
Fixes: dbb751ff ("fs: dlm: parallelize lowcomms socket handling")
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>