TYPO3 Core

After setting pageNotFound_handling in the localconf.php, hidden pages break the process of publishing pages to static HTML.

To reproduce:

1) make a page that has as least one hidden page as a child, and several regular pages

2) publish this page +1 sublevel

You will get the following error, and the pages are not written as static HTML:

Warning: Cannot modify header information - headers already sent by (output started at /Library/WebServer/Documents/www.blender3d.org/typo3_src-3.6.1/typo3/sysext/cms/tslib/index_ts.php:439) in /Library/WebServer/Documents/www.blender3d.org/typo3_src-3.6.1/typo3/sysext/cms/tslib/class.tslib_fe.php on line 992

Warning: Cannot modify header information - headers already sent by (output started at /Library/WebServer/Documents/www.blender3d.org/typo3_src-3.6.1/typo3/sysext/cms/tslib/index_ts.php:439) in /Library/WebServer/Documents/www.blender3d.org/typo3_src-3.6.1/typo3/sysext/cms/tslib/class.tslib_fe.php

After looking at the code, it would seem that the hidden page qualifies as a 'page not found', a HTTP header to redirect to the defined PageNogFound_handling page is performed and after that the process breaks.
(issue imported from #M665)