fix bug: not dumping a new blocks after fork

The problem described in psql_tools bug: psql_tools#16 (closed) After investigation, it was realized that it is an issue in sql_serializer code. During development, there was a problem with redundant calling by the processor's function 'block_num_rendezvous_trigger::report_complete_thread_stage', the problem was masked temporary by adding variable m_already_commited_blocks and was forgotten to remove. The redundant event was caused by triggering data processor with no data when the plugin was closed or reindex was finished.