implement snap back

Only works on Windows. In Linux this is disabled.

src/ui/bigtext/BigScrollBar.py

@@ -118,6 +118,7 @@ class BigScrollBar(QWidget):
 
         if self.pressedControl == QStyle.SubControl.SC_ScrollBarSlider:
             self.click_offset = click.y() - sr.y()
+            self.snap_back_position = self.value
 
         if (self.pressedControl == QStyle.SubControl.SC_ScrollBarAddPage
             or self.pressedControl == QStyle.SubControl.SC_ScrollBarSubPage) \