fixed crash when changing theme after closing tab

src/widgets/basewidget.hpp

@@ -20,6 +20,7 @@ public:
     explicit BaseWidget(singletons::ThemeManager &_themeManager, QWidget *parent,
                         Qt::WindowFlags f = Qt::WindowFlags());
     explicit BaseWidget(BaseWidget *parent, Qt::WindowFlags f = Qt::WindowFlags());
+    virtual ~BaseWidget();
 
     singletons::ThemeManager &themeManager;
 
@@ -49,6 +50,8 @@ private:
 
     std::vector<BaseWidget *> widgets;
 
+    pajlada::Signals::Connection themeConnection;
+
     static void setScaleRecursive(float scale, QObject *object);
 
     friend class BaseWindow;