This fixes both the long standing problem with the emptying of the session.xml file by forced Windows Update restart/shutdown and some potential Notepad++ crashes caused by possible main Notepad++ window blocking at exit.
Two main changes to the original design:
- WM_QUERYENDSESSION is not used anymore for the tidy-up ops and it always quickly returns TRUE/FALSE to the system as it should.
- there is now a safe-guard flag for the session.xml saving at N++ exit, which prevents otherwise possible incorrect overwriting in case of multiple "endsession" messages.
Fix#9850, fix#12389, close#12388