This doesn't work out of the box via SwRangeRedline::SetStart/End,
because the range of the redline is adjusted when redlining is disabled
by sw::DocumentRedlineManager::AppendRedline() when it compresses the
insert and delete redlines into a single reduced insert redline, and
then the redline is updated implicitly via SwIndex.

Change-Id: I4b652348b256df75e4c774ea5f3fdd78f59deb01
Reviewed-on: https://gerrit.libreoffice.org/28454Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>