BUG: Unable to create a List from a SLList

On beahlf of @hjasak

The following code fails

int main(int argc, char *argv[])
{
    SLList<label> a;
    List<label> b(a);

    return 0;
}

With the error message

src/OpenFOAM/lnInclude/ListI.H:94:35: error: invalid type argument of unary '*' (have 'int')
             this->operator[](i) = *iter;