Bug#31462844: ASSERTION `INITED == NONE || TABLE->OPEN_BY_HANDLER' FAILED.

Description: If an entry is deleted from mysql.user table
             using DELETE statement, subsequent SHOW
             CREATE USER for the same user would cause
             server to halt.

             SHOW CREATE USER opens mysql.user table to
             read user comment. It performs index scan
             on the table to find the matching user entry.
             Upon success, comment is retrieved and
             SE is notified about end of index scan
             operation by calling ha_index_end(). However,
             if an entry is deleted from mysql.user using
             DELETE and if FLUSH PRIVILEGES is not
             executed yet, index scan would fail. In that
             case, a call to ha_index_end() was missing.
             This later lead to assertion failure when
             all opened tables are being closed.

Fix: Fixed the issue by adding missing ha_index_end() call.

RB: 24616

Author: harinvadodaria

sql/auth/acl_table_user.cc

@@ -2397,9 +2397,11 @@ bool read_user_application_user_metadata_from_table(
   key_copy(user_key, table->record[0], table->key_info,
            table->key_info->key_length);
   if (table->file->ha_index_read_idx_map(table->record[0], 0, user_key,
-                                         HA_WHOLE_KEY, HA_READ_KEY_EXACT))
+                                         HA_WHOLE_KEY, HA_READ_KEY_EXACT)) {
+    table->file->ha_index_end();
     return false;  // technically we fail, but result should be an empty out
                    // string
+  }
   char *attributes_field =
       get_field(&tmp_mem, table->field[MYSQL_USER_FIELD_USER_ATTRIBUTES]);
   /*