Issue Description:

Example:

func testCrash() -> Any? {

    func capture(closure: () -> Void) {
        closure()
    }

    // implicity unwrap `object` and this won't crash...
    var object: Any
    var aClosure: () -> Void

    if true {
        return nil
    }

    object = ()

    // remove this double closure and it won't crash...
    aClosure = {
        capture {
            print(object)
        }
    }
    //

    return object
}

This is a simplified version of an actual use case. I get a bad access exception when returning nil in the function above, however if the nested closures further down the function are removed it all works correctly.

Also, if I implicitly unwrap `object` in the function above at declaration it will also work correctly.

I tested this with multiple different compiler optimisation levels and in a playground and it failed each time.