staging/lustre/ldlm: fix NULL pointer dereference

Pointer '*exp' returned from call to function 'class_conn2export'
at line 523 may be NULL and may be dereferenced at line 543.
Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-on: http://review.whamcloud.com/9323
ntel-bug-id: https://jira.hpdd.intel.com/browse/LU-4629Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/ldlm/ldlm_lib.c

@@ -514,7 +514,7 @@ int client_connect_import(const struct lu_env *env,
 		LASSERT (imp->imp_state == LUSTRE_IMP_DISCON);
 		GOTO(out_ldlm, rc);
 	}
-	LASSERT((*exp)->exp_connection);
+	LASSERT(*exp != NULL && (*exp)->exp_connection);
 
 	if (data) {
 		LASSERTF((ocd->ocd_connect_flags & data->ocd_connect_flags) ==