crash in selecting text in comments midway in para

(cherry picked from commit 7dca5341d799d59a81e6dac84586fa2daa02a550)

Conflicts:
	sw/source/core/uibase/shells/langhelper.cxx

Change-Id: Iaab71e201fae6a03936ccc6aac040027a183209c
Reviewed-on: https://gerrit.libreoffice.org/9148
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>