Event handler leak on noData queries

[andvgal]

Obviously it's not the purpose of pg-cursor, but sometimes you do not know type of query in advance, but need to implement a common query execution logic.

If noData (INSERT/UPDATE/DELETE without RETURNING clause) queries are run through cursor then dangling rowDescription events are left on connection. It leads to Node,js memory leak warning.

Simple solution is to clear rowDescription on noData event, like:

  const ifNoData = () => {
    this.state = 'idle'
    this._shiftQueue()
    con.removeListener('rowDescription', onRowData)
  }

  const onRowData = () => {
    con.removeListener('noData', ifNoData)
  }

  if (this._conf.types) {
    this._result._getTypeParser = this._conf.types.getTypeParser
  }

  con.once('noData', ifNoData)
  con.once('rowDescription', onRowData)

However, it seems the code is not completely safe. We need to ensure that all introduced event handlers are removed upon cursor close by (error, noData, done, forced close, etc.)