Fix nonempty variadic parameters declared in body

For nonempty variadic parameters that were declared in the body, like this:

    void f(elems) {
        String+ elems;
        // ...
    }

the TypeVisitor forgot to carry over the atLeastOne information from the
SequencedType.
Merge pull request #1000 from lucaswerkmeister/fixNonemptyVariadicInBody

Fix nonempty variadic parameters declared in body