ox-icalendar: Fix `org-icalendar-blocked-headline-p'
* lisp/ox-icalendar.el (org-icalendar-blocked-headline-p): Only
consider children when looking for blocked entries, not the headline
itself.
Reported-by: Duane Farnsworth <dfarnsworth@clarion.edu>
<http://lists.gnu.org/r/emacs-orgmode/2019-02/msg00275.html>