Fix row and col size in MatrixBuilder<MultiTypeMatrix<...>>

Row and col size heb been swapped before leading to incorrect results
for non-square outer matrix pattern.

dune/fufem/assemblers/istlbackend.hh

@@ -184,7 +184,7 @@ private:
   //! number of multi type cols (we assume the matrix is well-formed)
   static constexpr size_t colBlocks_ = Matrix::M();
   //! 2D array of IndexSets
-  std::array<std::array<Dune::MatrixIndexSet,rowBlocks_>,colBlocks_> indices_;
+  std::array<std::array<Dune::MatrixIndexSet,colBlocks_>,rowBlocks_> indices_;
   Matrix& matrix_;
 };