Type guard fails to narrow type with generic parameters #1943

class C
{
    foo: number;
}
function foo (x : C | Array<C>) : C
{
    if (x instanceof C)
      return x;
    return x[0];
}

class C<A>
{
    foo: A;
}
function foo<A> (x : C<A> | Array<C<A>>) : C<A>
{
    if (x instanceof C)
      return x;
    return x[0];
}