ui: fix crash when closing configure window

This crash happens 100% of the time (on Linux at least), you just need
to open the configure window and click OK.

It seems to happen when the tabs are destroyed and once all the tabs are
destroyed, a final signal is sent with `index == -1`. So `debug_tab_tab`
doesn't exist anymore when this happens, so the crash.

src/yuzu/configuration/configure_dialog.cpp

@@ -81,8 +81,11 @@ ConfigureDialog::ConfigureDialog(QWidget* parent, HotkeyRegistry& registry,
     SetConfiguration();
     PopulateSelectionList();
 
-    connect(ui->tabWidget, &QTabWidget::currentChanged, this,
-            [this]() { debug_tab_tab->SetCurrentIndex(0); });
+    connect(ui->tabWidget, &QTabWidget::currentChanged, this, [this](int index) {
+        if (index != -1) {
+            debug_tab_tab->SetCurrentIndex(0);
+        }
+    });
     connect(ui_tab.get(), &ConfigureUi::LanguageChanged, this, &ConfigureDialog::OnLanguageChanged);
     connect(ui->selectorList, &QListWidget::itemSelectionChanged, this,
             &ConfigureDialog::UpdateVisibleTabs);