This problem can be reproduced with the bugdoc from fdo#60234, by
dragging and dropping the lower left drawing object.
The ATK bridge is notified of the change, and updates its list of
children by calling getAccessibleChildCount() and then
getAccessibleChild() in a loop.  Unfortunately the count returned does
not match the available children (the difference is the object that is
being dragged).  The implementations in
SwAccessibleFrame::GetChildCount() and SwAccessibleFrame::GetChild()
use slightly different iterators for the SwPageFrm, and the
SwAccessibleChildMap one is implemented as a std::map, using the OrdNum
of the drawing object as a key.  On the dragged object, that OrdNum has
been reset to 0 in RemoveFlyFromPage, but it is still in the pSortedObjs
of the SwPageFrm, and so it is not inserted into the map, and iteration
over the map is missing one element.

149     return _SwAccessibleChildMap::insert( aEntry );
Value returned is $22 = {first = {first = {eLayerId =
SwAccessibleChildMapKey::HELL, nOrdNum = 0}, second = ...}, second = false}

Fix this by removing the object from pSortedObjs before disposing
the a11y frames.

Change-Id: I4e4bb37759382e32150cff6def02d80a55e4a702