Destroy chain_controller during chain_plugin shutdown
Destroy chain_controller during chain_plugin shutdown

When running a node sending hundreds of transactions a second, Ctrl-Cing it will typically crash. Destroy the chain_controller during chain_plugin::plugin_shutdown() to ensure better cleanup.

EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos