Fix crash when forwarding incidence via context menu
The MailClient inside ITIPHandler may work asynchronously, causing the ITIPHandler inside the KOEVentPopupMenu to go out-of-scope and be destroyed before the async operation in the MailClient finishes. Since MailClient relies on a factory object owned by the ITIPHandler, if the ITIPHandler gets destroyed before the MailClient finishes, it will delete the factory object causing use-after-free when the async operation in MailClient is finally done.
FIXED-IN: 23.08.3