fix crash calling nonexistent delegate (also memory leak)

[gobbledegook]

This is a patch that fixes issue #19

[Coeur]

As present bdkjones repo is not maintained anymore, and as I am a maintainer for a fork of VDKQueue, I thank you for the suggested fix. I decided to implement it differently, without needing any new method: https://github.com/transmission/transmission/pull/6290