Disconnect event not caught

see https://github.com/mariadb-corporation/mariadb-connector-nodejs/issues/195

The 3.0.0 release seems to have introduced a bug that wasn't there in 2.5.6.

Scenario

Using the promise API

• Create a connection pool
• Get a connection
• Perform some requests
• Release connection
• Shutdown the DB server

• Error ER_CONNECTION_KILLED is sometimes caught in the error event of the connection, sometimes not
• Error ER_SOCKET_UNEXPECTED_CLOSE is sometimes caught in the error event of the connection, sometimes not
• One more ER_SOCKET_UNEXPECTED_CLOSE is raised but I'm unable to catch it, thus my node process crashes. It doesn't get caught by the error event handler that I added to the connection.