When having DataGrid with multiple editable columns the
CollectionEvent UPDATE should be sent when then row is changed
(DataGridEvent.ITEM_EDIT_END reason !=
DataGridEventReason.NEW_COLUMN) otherwise the disableAutoUpdate is
called preventing the UPDATE event to be triggered..
the problem is that once the row is changed
the enableAutoUpdate is called
(DataGrid.as:4814) causing the UPDATE CollectionEvent to be
the currently edited value is
another UPDATE event fired
this patch forces the UPDATE event to be fired just once for
the row after the last edited value has been commited.