Two related fixes for FooterBar to snap to bounds

- The first fix solves the issue that the FooterBar gets stuck somewhere
  in the middle when it is released when not swiping (i.e. without vertical
  velocity).
- The second fix solves the issue that happens when the window is
  resized while the FooterBar is opened.  In that case, the FooterBar
  can also get stuck being partially opened.