Make sure callback happens if a model is not attached to the data source

/to @bajtos or @ritch 

The PR fixes a hang issue during `automigrate` if one of the models is not attached to the data source.

I'll add a test in connectors.
Interesting, that looks like a bug to me. With a large enough array, it is a recipe for stack overflow error. Anyways, that's out of scope of this PR.