disposed but not dtored

just die when you are supposed to, without this endless amounts of accessiblity
cells remain after sorting slides with tables in them

Change-Id: Ice9a86b8b806e58f9bf871341a38f7729798dda9

svx/source/table/accessibletableshape.cxx

@@ -132,6 +132,7 @@ void AccessibleTableShapeImpl::dispose()
         {
             (*iter).second->dispose();
         }
+        maChildMap.clear();
         Reference< XModifyListener > xListener( this );
         mxTable->removeModifyListener( xListener );
         mxTable.clear();