qml: rbf/cancel: abort update if adding tx info fails

Early return the update() methods of QETxRbfFeeBumper and QETxCanceller
if it fails to fetch missing tx information from the Network to prevent
an exception in `Abstract_Wallet.bump_fee()` and
`Abstract_Wallet.dscancel()`. See
https://github.com/spesmilo/electrum/issues/5502#issuecomment-40213084270

electrum/gui/qml/qetxfinalizer.py

@@ -758,6 +758,13 @@ class QETxRbfFeeBumper(TxFeeSlider, TxMonMixin):
             self.validChanged.emit()
             self.warning = _("The new fee rate needs to be higher than the old fee rate.")
             return
+
+        if not self._orig_tx.add_info_from_wallet_and_network(wallet=self._wallet.wallet, show_error=self._logger.error):
+            self._valid = False
+            self.validChanged.emit()
+            self.warning = _("Transaction is missing info from network")
+            return
+
         try:
             self._tx = self._wallet.wallet.bump_fee(
                 tx=self._orig_tx,
@@ -877,6 +884,12 @@ class QETxCanceller(TxFeeSlider, TxMonMixin):
             self.warning = messages.MSG_RELAYFEE
             return
 
+        if not self._orig_tx.add_info_from_wallet_and_network(wallet=self._wallet.wallet, show_error=self._logger.error):
+            self._valid = False
+            self.validChanged.emit()
+            self.warning = _("Transaction is missing info from network")
+            return
+
         try:
             self._tx = self._wallet.wallet.dscancel(
                 tx=self._orig_tx,