gui: ensure external signer option remains disabled without signers

When no external signers are available, the option to enable external
signers should always be disabled. However the encrypt wallet checkbox
can erroneously re-enable the external signer checkbox. To avoid this,
CreateWalletDialog now stores whether signers were available during
setSigners so that future calls to external_signer_checkbox->setEnabled
can account for whether signers are available.

Github-Pull: bitcoin-core/gui#396
Rebased-From: a9b9ca8

src/qt/createwalletdialog.cpp

@@ -32,7 +32,7 @@ CreateWalletDialog::CreateWalletDialog(QWidget* parent) :
         // set to true, enable it when isEncryptWalletChecked is false.
         ui->disable_privkeys_checkbox->setEnabled(!checked);
 #ifdef ENABLE_EXTERNAL_SIGNER
-        ui->external_signer_checkbox->setEnabled(!checked);
+        ui->external_signer_checkbox->setEnabled(m_has_signers && !checked);
 #endif
         // When the disable_privkeys_checkbox is disabled, uncheck it.
         if (!ui->disable_privkeys_checkbox->isEnabled()) {
@@ -115,7 +115,8 @@ CreateWalletDialog::~CreateWalletDialog()
 
 void CreateWalletDialog::setSigners(const std::vector<ExternalSigner>& signers)
 {
-    if (!signers.empty()) {
+    m_has_signers = !signers.empty();
+    if (m_has_signers) {
         ui->external_signer_checkbox->setEnabled(true);
         ui->external_signer_checkbox->setChecked(true);
         ui->encrypt_wallet_checkbox->setEnabled(false);

src/qt/createwalletdialog.h

@@ -35,6 +35,7 @@ class CreateWalletDialog : public QDialog
 
 private:
     Ui::CreateWalletDialog *ui;
+    bool m_has_signers = false;
 };
 
 #endif // BITCOIN_QT_CREATEWALLETDIALOG_H