Fix callable not clearing freed pointer

[rune-scape]

fixes a crash i had on shutdown,,
but it happens anytime a callable with a custom pointer is copy-assigned a regular callable, then destructed
manual reference counting and memory managment should rlly be abstracted or avoided to prevent silly crashes like this

[akien-mga]

Thanks!

[DanielSnd]

I've had an annoying crash when closing my games on mac forever, after this merge it's gone, thank you!