fdo#73695 prevent use of invalidated iterator due to re-entrance

... through the UNO backdoor..
While charts are updated there can be chart data listeners in BASIC that
in turn modify things such that charts are inserted/removed from the
listener chain, invalidating the iterator. If that happens break and
bail out instead of crashing. Not ideal, but..

Change-Id: Iefb33d3a96d79caed0ee4e19b73e8f811ef3d937