gui: Call setWalletActionsEnabled(true) only for the first wallet

Summary:
> On master there is a bug:
>  - open an encrypted wallet; please note that the "Encrypt Wallet..." menu item is disabled that is expected
>  - then open any other wallet; note that the "Encrypt Wallet..." menu item gets enabled that is wrong
> This PR fixes this bug.

This is a backport of [[bitcoin-core/gui#43 | core-gui#43]]

Test Plan:
`ninja all check-all`

Failed to reproduce the bug after this change.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10604

Author: hebasto

src/qt/bitcoingui.cpp

@@ -761,14 +761,15 @@ void BitcoinGUI::addWallet(WalletModel *walletModel) {
     if (!walletFrame->addWallet(walletModel)) {
         return;
     }
-    const QString display_name = walletModel->getDisplayName();
-    setWalletActionsEnabled(true);
     rpcConsole->addWallet(walletModel);
-    m_wallet_selector->addItem(display_name, QVariant::fromValue(walletModel));
-    if (m_wallet_selector->count() == 2) {
+    if (m_wallet_selector->count() == 0) {
+        setWalletActionsEnabled(true);
+    } else if (m_wallet_selector->count() == 1) {
         m_wallet_selector_label_action->setVisible(true);
         m_wallet_selector_action->setVisible(true);
     }
+    const QString display_name = walletModel->getDisplayName();
+    m_wallet_selector->addItem(display_name, QVariant::fromValue(walletModel));
 }
 
 void BitcoinGUI::removeWallet(WalletModel *walletModel) {