Add a comment and move if statements into braces

include/deal.II/matrix_free/hanging_nodes_internal.h

@@ -381,13 +381,20 @@ namespace internal
       // on a level coarser than the finest one.
       bool all_cells_on_same_level = true;
       for (const auto &cell : triangulation.active_cell_iterators())
-        if (cell->level() == static_cast<int>(triangulation.n_levels()) - 1)
-          break;
-        else if (!cell->is_artificial())
-          {
-            all_cells_on_same_level = false;
+        {
+          // If we reached the finest level and still not found a
+          // non-artificial cell, we do not have cells on different level, and
+          // hence we can stop.
+          if (cell->level() == static_cast<int>(triangulation.n_levels()) - 1)
             break;
-          }
+          else if (!cell->is_artificial())
+            {
+              // We found a cell that has not triggered the other `if` above,
+              // so we are a level coarser than other cells
+              all_cells_on_same_level = false;
+              break;
+            }
+        }
       if (all_cells_on_same_level)
         return;