final nit

Co-authored-by: Ralf Jung <[email protected]>

src/borrow_tracker/tree_borrows/tree.rs

@@ -642,6 +642,7 @@ impl<'tcx> Tree {
             // Record whether we did any change; if not, the invariant is restored and we can stop the traversal.
             let mut any_change = false;
             for (_, map) in self.rperms.iter_mut_all() {
+                // Check if this node has a state for this location (or range of locations).
                 if let Some(perm) = map.get_mut(current) {
                     // Update the per-location SIFA, recording if it changed.
                     any_change |=