wallet: fix rbf_batching edge case

The old change output was given to coinchooser
as part of possible UTXOs to use.
(Though the coinchooser was really unlikely to select it, as by
definition that UTXO is unconfirmed)

electrum/wallet.py

@@ -732,6 +732,8 @@ class Abstract_Wallet(AddressSynchronizer):
             # If there is an unconfirmed RBF tx, merge with it
             base_tx = self.get_unconfirmed_base_tx_for_batching()
             if config.get('batch_rbf', False) and base_tx:
+                # make sure we don't try to spend change from the tx-to-be-replaced:
+                coins = [c for c in coins if c['prevout_hash'] != base_tx.txid()]
                 is_local = self.get_tx_height(base_tx.txid()).height == TX_HEIGHT_LOCAL
                 base_tx = Transaction(base_tx.serialize())
                 base_tx.deserialize(force_full_parse=True)