GH-2119 Update group view scrollbar when the size of rows doesn't change

Previously, it would only update when you resize the window horizontally
enough to change the number of icons that fit in a row.

application/groupview/GroupView.h

@@ -96,6 +96,8 @@ protected:
 
 	void startDrag(Qt::DropActions supportedActions) override;
 
+	void updateScrollbar();
+
 private:
 	friend struct VisualGroup;
 	QList<VisualGroup *> m_groups;