scsi: libiscsi: Fix NULL pointer dereference in iscsi_eh_session_reset

This commit addresses NULL pointer dereference in iscsi_eh_session_reset.
Reference should not be made to session->leadconn when session->state is
set to ISCSI_STATE_TERMINATE.

Signed-off-by: Fred Herard <fred.herard@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>