dynamic_cast a rvalue-reference unique_ptr?

I have a class Base and a derived class Derived. A function reads objects from a file descriptor and returns Base objects:

std::unique_ptr<Base> readNextThing();

And in some place I need to upcast the return value of this function to Derived. This is relevant since the input unique_ptr is a rvalue-reference, so we don't copy the pointer, but move it. In this specific context I don't mind the object being destroyed if it's not of Derived subtype, I just need to detect that the downcast pointer is null in that case.

I could do:

template<typename T, typename U>
std::unique_ptr<T> dynamic_unique_cast(std::unique_ptr<U> && unique)
{
    T * t = dynamic_cast<T*>(unique.get());
    if(t) { unique.release(); }  //Transfer ownership
    return std::unique_ptr<T>(t);
}

and

std::unique_ptr<Derived> d = dynamic_unique_cast<Derived>(readNextThing());

1. Is there a built-in function for doing this?
2. Is there any risk of memory leak in the above code if an exception occurs?