Bug 740471 -  Applying payment to invoice Segmentation fault

Attempt to fix it by no longer nullifying lots during processing
Bug 740471 -  Applying payment to invoice Segmentation fault

Clear selection before emptying list store to prevent
the code from running calculations on a changing list.
Bug 740471 -  Applying payment to invoice Segmentation fault

Stop listening for gui update events while on the way out
(after the ok button was pressed).