qt: update widgets availability on wallet selection

The Transaction View should be only enabled when a wallet is selected.
Therefore it has been added a condition for a selected wallet on
enableHistoryAction() since its availability also depends on the mask
value checkbox.

src/qt/bitcoingui.cpp

@@ -673,8 +673,10 @@ void BitcoinGUI::setClientModel(ClientModel *_clientModel, interfaces::BlockAndH
 #ifdef ENABLE_WALLET
 void BitcoinGUI::enableHistoryAction(bool privacy)
 {
-    historyAction->setEnabled(!privacy);
-    if (historyAction->isChecked()) gotoOverviewPage();
+    if (walletFrame->currentWalletModel()) {
+        historyAction->setEnabled(!privacy);
+        if (historyAction->isChecked()) gotoOverviewPage();
+    }
 }
 
 void BitcoinGUI::setWalletController(WalletController* wallet_controller, bool show_loading_minimized)