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.
2 jobs for master in 9 minutes and 34 seconds (queued for 184 minutes and 7 seconds)
Status Name Job ID Coverage
  Build
passed linux kf5-qt5 qt5.15 #105306

00:09:03

85.0%
passed reuse #105305

00:00:31