MDEV-29131 Assertion `status == 0' failed when renaming user after deleting table roles_mapping

if mysql.roles_mapping table doesn't exist (it's optional, after all),
we still update in-memory structures to keep them consistent

mysql-test/suite/roles/rename_user.result

@@ -25,3 +25,12 @@ newhost	test_user_rm	test_role1	N
 delete from mysql.roles_mapping;
 delete from mysql.user where user like 'test%';
 flush privileges;
+#
+# MDEV-29131 Assertion `status == 0' failed when renaming user after deleting table roles_mapping
+#
+create role r;
+rename table mysql.roles_mapping to test.t1;
+rename user current_user to a@a;
+rename user a@a to root@localhost;
+rename table test.t1 to mysql.roles_mapping;
+drop role r;

mysql-test/suite/roles/rename_user.test

@@ -36,3 +36,13 @@ delete from mysql.roles_mapping;
 delete from mysql.user where user like 'test%';
 flush privileges;
 
+--echo #
+--echo # MDEV-29131 Assertion `status == 0' failed when renaming user after deleting table roles_mapping
+--echo #
+create role r;
+rename table mysql.roles_mapping to test.t1;
+rename user current_user to a@a;
+rename user a@a to root@localhost;
+rename table test.t1 to mysql.roles_mapping;
+drop role r;
+

sql/sql_acl.cc

@@ -10153,11 +10153,9 @@ static int handle_grant_data(THD *thd, Grant_tables& tables, bool drop,
   }
 
   /* Handle roles_mapping table. */
-  if (tables.roles_mapping_table().table_exists())
-  {
-    if ((found= handle_grant_table(thd, tables.roles_mapping_table(),
-                                   ROLES_MAPPING_TABLE, drop,
-                                   user_from, user_to)) < 0)
+  if (tables.roles_mapping_table().table_exists() &&
+      (found= handle_grant_table(thd, tables.roles_mapping_table(),
+                         ROLES_MAPPING_TABLE, drop, user_from, user_to)) < 0)
   {
     /* Handle of table failed, don't touch the in-memory array. */
     result= -1;
@@ -10171,7 +10169,6 @@ static int handle_grant_data(THD *thd, Grant_tables& tables, bool drop,
     if (search_only)
       goto end;
   }
-  }
 
   /* Handle user table. */
   if ((found= handle_grant_table(thd, tables.user_table(), USER_TABLE,