cabana: fix slider crash on exit if loadThumbnails is running (#27052)

tools/cabana/videowidget.cc

@@ -133,6 +133,11 @@ Slider::Slider(QWidget *parent) : QSlider(Qt::Horizontal, parent) {
   QObject::connect(can, &AbstractStream::streamStarted, this, &Slider::streamStarted);
 }
 
+Slider::~Slider() {
+  abort_load_thumbnail = true;
+  thumnail_future.waitForFinished();
+}
+
 void Slider::streamStarted() {
   abort_load_thumbnail = true;
   thumnail_future.waitForFinished();

tools/cabana/videowidget.h

@@ -18,6 +18,7 @@ class Slider : public QSlider {
 
 public:
   Slider(QWidget *parent);
+  ~Slider();
 
 private:
   void mousePressEvent(QMouseEvent *e) override;