Segmentation fault (Access violation) in `test_cursor_async_io::test_many_batches_with_async_io`

[pacman82]

Saw this test_cursor_async_io::test_many_batches_with_async_io fail with access violation. Seems unrelated to code change, which triggered the build on appveyor.

https://ci.appveyor.com/project/MathMagique/turbodbc/builds/26533096/job/qwes783tnc283tl2