fix: widget bugs surfaced by new gtest coverage

- FrameRateComboBox: RepopulateList() left current index at -1 on first
  fill, so GetFrameRate() returned 0/1 instead of the displayed first
  entry until something called SetFrameRate()
- HandMovableView: default_drag_mode_ was never initialized; an early
  Core::ToolChanged signal would setDragMode() with it (UB)

app/widget/handmovableview/handmovableview.cpp

@@ -34,6 +34,7 @@ namespace olive
 HandMovableView::HandMovableView(QWidget *parent)
 	: super(parent)
 	, dragging_hand_(false)
+	, default_drag_mode_(NoDrag)
 	, is_timeline_axes_(false)
 {
 	connect(Core::instance(), &Core::ToolChanged, this,