Fix compiler warning

[NiklasWik]

Related to #13910 (comment)

Haven't tried to compile myself but I'm guessing this would work.

[peterrum]

Question: is it possible to have a 1D RT? If not one should probably also add here an assert!

[NiklasWik]

I think it is asserted in the class itself, but I might be mistaken

[peterrum]

There is no assert here:

dealii/include/deal.II/matrix_free/evaluation_kernels.h

Lines 3555 to 3557 in ecdd5f2

	if (shape_info.element_type == MatrixFreeFunctions::tensor_raviart_thomas)
	interpolate_generic_raviart_thomas<do_evaluate, add_into_output>(
	n_components, input, output, flags, face_no, shape_info);

[NiklasWik]

This is the one I was referring to

dealii/source/fe/fe_raviart_thomas_nodal.cc

Line 445 in ecdd5f2

Assert(dim >= 2, ExcImpossibleInDim(dim));

[kronbichler]

/rebuild

[kronbichler]

This looks good, let us merge it soon and see if the outcome is as desired.

[marcfehling]

Suggested change

	if (dim == 1)
	return;
	if (dim == 1)
	{
	Assert(false, ExcInternalError());
	return;
	}

As you said, as this condition should never be met, I would suggest to clarify this be adding another assertion here right before the return statement. If you want to, you could add another in-source comment to why this return statement is necessary.