MDEV-8614 Assertion `status == 0' failed in add_role_user_mapping_action on RENAME USER

don't forget to re-examine the current element when updating a HASH

mysql-test/suite/roles/rebuild_role_grants.result

@@ -56,3 +56,9 @@ Host	User	Role	Admin_option
 localhost	root	r1	Y
 drop role r1;
 drop user u2;
+create user foo@localhost;
+grant create user on *.* to foo@localhost;
+create role look, isp, xxx, ppp;
+rename user current_user to nnnn@'%';
+drop role look, isp, xxx, ppp;
+drop user nnnn@'%';

mysql-test/suite/roles/rebuild_role_grants.test

@@ -54,3 +54,16 @@ select * from mysql.roles_mapping;
 
 drop role r1;
 drop user u2;
+
+#
+# MDEV-8614 Assertion `status == 0' failed in add_role_user_mapping_action on RENAME USER
+#
+create user foo@localhost;
+grant create user on *.* to foo@localhost;
+--connect (con1, localhost, foo,,)
+create role look, isp, xxx, ppp;
+rename user current_user to nnnn@'%';
+drop role look, isp, xxx, ppp;
+connection default;
+disconnect con1;
+drop user nnnn@'%';

sql/sql_acl.cc

@@ -8977,8 +8977,7 @@ static int handle_grant_struct(enum enum_acl_lists struct_no, bool drop,
             So we need to examine the current element once again, but
             we don't need to restart the search from the beginning.
           */
-          if (idx != elements)
-            idx++;
+          idx++;
           break;
         }
 
@@ -9010,6 +9009,7 @@ static int handle_grant_struct(enum enum_acl_lists struct_no, bool drop,
 
           my_hash_update(roles_mappings_hash, (uchar*) role_grant_pair,
                          (uchar*) old_key, old_key_length);
+          idx++; // see the comment above
           break;
         }