out-of-bounds string access

... when parsing  ='foo'#  with no character following.

Change-Id: Id65fce721cb47a4d3c947c677323bdcaa2ce957f
(cherry picked from commit 07b18860ae03ecb66b5605201f34c2aef3a55ad6)
Reviewed-on: https://gerrit.libreoffice.org/11062
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>