Fix previous crashes when scrolling generic version

   of wxDataViewCtrl.
  Added in-place editing of strings (no user vetoing
   and such). The code uses the corrected version of
   the respective code from wxListCtrl.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38452 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775