trivial mixed expression throw bad_function call

this throws a bad_function_call and gdb says "no stack" =/. Failing test is in #62

    TEST_CASE("bad_function_call")
    {

        zdispatcher_t<detail::plus, 2>::init();


        auto x0 = xarray<int>::from_shape({2,2});
        auto x1 = xarray<int>::from_shape({2,2});

        zarray z0(x0);
        zarray z1(x1);

        auto res = xarray<double>::from_shape({2,2});
        zarray zres(res);

        zres =  x0 + x1;

    }

without the explicit init I get a "callback not found" exception as expected

mhh...just realized that the code above does not add the zarrays but the normal xarrays. Still interesting. when I add some more dispatcher-inits I get some other error:

this give a callback not found

    TEST_CASE("bad_function_call")
    {

        zdispatcher_t<detail::plus, 2>::init();
        zdispatcher_t<detail::xassign_dummy_functor, 1>::init();
    
        auto x0 = xarray<int>::from_shape({2,2});
        auto x1 = xarray<int>::from_shape({2,2});

        zarray z0(x0);
        zarray z1(x1);

        auto res = xarray<double>::from_shape({2,2});
        zarray zres(res);

        zres =  x0 + x1;

    }

this also give a callback not found (this time we actually add the zarrays)

    TEST_CASE("bad_function_call")
    {

        zdispatcher_t<detail::plus, 2>::init();
        zdispatcher_t<detail::xassign_dummy_functor, 1>::init();
    
        auto x0 = xarray<int>::from_shape({2,2});
        auto x1 = xarray<int>::from_shape({2,2});

        zarray z0(x0);
        zarray z1(x1);

        auto res = xarray<double>::from_shape({2,2});
        zarray zres(res);

        zres =  z0 + z1;

    }