message: fix wrong assert
diff: @@ -188,7 +188,7 @@ impl StagingTransaction {
  pub fn remove_input(&mut self, txin: TxIn) -> append::Result<()> {
  // we can only remove existing inputs
  assert!(
  - self.transaction.lookup_input(txin.clone()).is_none(),
  + self.transaction.lookup_input(txin.clone()).is_some(),
  "cannot remove input, it is not present in the transaction ({:#?})",
  txin
  );
  