ref: a005abe2701b878770544e2e09f41ab9e2a399e7
parent: 709cb723bba3aa43ba40a5c70dba0b337bae54e2
author: Sigrid Solveig Haflínudóttir <ftrvxmtrx@gmail.com>
date: Tue Dec 15 17:30:13 EST 2020
ivfclose: be safer, set stuff to nil to support repeated calls