Fix popdown of Error/Help dialog through window-close button

Fix popdown of Error/Help dialog through window-close button

Closing an Error popup that was a daughter of another dialog (as Help
dialogs would often be) through the window-close button instead of 'OK'
would permanently block popdown of the parent dialog, because the info
that the Error dialog was still up would not have been reset by the Error
dialog's OK function. GenericPopDown now calls the OK function of such
a dialog (actually FatalDlg) even on a REJECT response.