message: Fix bug where adding node to csr graph stole existing edges
diff: @@ -269,7 +269,7 @@ impl<N, E, Ty, Ix> Csr<N, E, Ty, Ix>
  /// Adds a new node with the given weight, returning the corresponding node index.
  pub fn add_node(&mut self, weight: N) -> NodeIndex<Ix> {
  let i = self.row.len() - 1;
  - self.row.insert(i, 0);
  + self.row.insert(i, self.column.len());
  self.node_weights.insert(i, weight);
  Ix::new(i)
  }
  