Android: Disable "Make [NDK] default" button while NDKs list is empty

When pressing the "Make [NDK] Default" button while the list is empty
leads to a crash. The button should actually not be enabled if the list
is empty.

This change disables the button while the NDKs list is empty.

Fixes: QTCREATORBUG-30716
Change-Id: I5f10fd180f62d20210f1b0c0261e4d821d0582dd
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/android/androidsettingswidget.cpp

@@ -813,6 +813,7 @@ void AndroidSettingsWidget::updateUI()
         }
     }
 
+    m_makeDefaultNdkButton->setEnabled(m_ndkListWidget->count() > 0);
     m_makeDefaultNdkButton->setText(isDefaultNdkSelected() ? Tr::tr("Unset Default")
                                                            : Tr::tr("Make Default"));
 }