Access violation in CUITransactionDlg::ItemCountOK()

[twostars]

This is a repost of #80 specifically addressing the access violation caused by CUITransactionDlg::ItemCountOK() as in the screenshot here:

This is caused by the icon no longer being set when expected.
Without looking at it too deeply, this is most likely due to an interaction that should otherwise be blocked (usually UI interactions are blocked between server requests, so item changes cannot be made to cause things to break like this).