gui: bumpfee signer support

Specifically this enables the Send button in the fee bump dialog for wallets with external signer support. Similar to 2efdfb88aa.

src/qt/walletmodel.cpp

@@ -508,7 +508,9 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
         questionString.append(tr("Warning: This may pay the additional fee by reducing change outputs or adding inputs, when necessary. It may add a new change output if one does not already exist. These changes may potentially leak privacy."));
     }
 
-    auto confirmationDialog = new SendConfirmationDialog(tr("Confirm fee bump"), questionString, "", "", SEND_CONFIRM_DELAY, !m_wallet->privateKeysDisabled(), getOptionsModel()->getEnablePSBTControls(), nullptr);
+    const bool enable_send{!wallet().privateKeysDisabled() || wallet().hasExternalSigner()};
+    const bool always_show_unsigned{getOptionsModel()->getEnablePSBTControls()};
+    auto confirmationDialog = new SendConfirmationDialog(tr("Confirm fee bump"), questionString, "", "", SEND_CONFIRM_DELAY, enable_send, always_show_unsigned, nullptr);
     confirmationDialog->setAttribute(Qt::WA_DeleteOnClose);
     // TODO: Replace QDialog::exec() with safer QDialog::show().
     const auto retval = static_cast<QMessageBox::StandardButton>(confirmationDialog->exec());
@@ -526,6 +528,7 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
 
     // Short-circuit if we are returning a bumped transaction PSBT to clipboard
     if (retval == QMessageBox::Save) {
+        // "Create Unsigned" clicked
         PartiallySignedTransaction psbtx(mtx);
         bool complete = false;
         const TransactionError err = wallet().fillPSBT(SIGHASH_ALL, false /* sign */, true /* bip32derivs */, nullptr, psbtx, complete);
@@ -541,7 +544,7 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
         return true;
     }
 
-    assert(!m_wallet->privateKeysDisabled());
+    assert(!m_wallet->privateKeysDisabled() || wallet().hasExternalSigner());
 
     // sign bumped transaction
     if (!m_wallet->signBumpTransaction(mtx)) {