umbrello/umlwidgets/umlwidget.cpp fix for crash on removing association:

- In function adjustAssocs, if both dx and dy are near 0 then do not
  enter loop over associationwidget list for calling widgetMoved() on
  each assocwidget.
  Reason: Doing so eventually leads to call of calculateEndingPoints()
  on the very associationwidget currently being removed, resulting in
  crash.