Fix lib panic on insert_many

[j-mendez]

This removes the panic that happens on insert many.
We should not have panics in a library production code.

[tyt2y3]

sorry, I don't think this is a proper fix, yes it removes the panic, but the resulting query will still be wrong.
ideally, we'd have to loop over the models a second time with a complete list of all columns to constuct the insert statement