The problem here is presumably that the parser thread reports a
low-level SAX exception and the main thread reports a high-level filter
exception at the same time, so both threads modify maSavedException
concurrently.

Change-Id: Ic8ce9a4992208a24a111c990a67be163858ddaf8
Reviewed-on: https://gerrit.libreoffice.org/47478Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Jenkins <ci@libreoffice.org>
(cherry picked from commit 2a88f62a)
Reviewed-on: https://gerrit.libreoffice.org/47539