tabbox: Add desktop window to client list only if "show desktop mode" enabled

Previously, we always added the desktop to the client list when the list
was empty. We added it even if the switcher's "show desktop mode" was
disabled.

Now, we only add the desktop to the client list if the switcher's "show
desktop mode" is enabled.

src/tabbox/clientmodel.cpp

@@ -224,7 +224,7 @@ void ClientModel::createClientList(bool partialReset)
     }
 
     if (tabBox->config().clientApplicationsMode() != TabBoxConfig::AllWindowsCurrentApplication
-        && (tabBox->config().showDesktopMode() == TabBoxConfig::ShowDesktopClient || m_mutableClientList.isEmpty())) {
+        && tabBox->config().showDesktopMode() == TabBoxConfig::ShowDesktopClient) {
         Window *desktopClient = tabBox->desktopClient();
         if (desktopClient) {
             m_mutableClientList.append(desktopClient);