improve parse error recovery paths

to reduce collateral damage from parse errors.

(cherry picked from qtcreator/00c0d0d5e42d28e03c2846c17d3acbcd8420859d)
Change-Id: Ic59700d657069d3b15372509b4bff966057d27a9
Reviewed-by: Qt Doc Bot <qt_docbot@qt-project.org>
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>
(cherry picked from qtbase/ae3f95a951334dee001e37c305e4d7bf91c0d1b3)
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>