It's possible that an ODF document contains redlines that will be
deduplicated by CompressRedlines().

If that happens during some editing operation, then a SwRedline
will be deleted and the nodes array becomes smaller by at least 3
nodes; any Undo actions that were created prior to the operation
that called CompressRedlines() will store invalid node indexes now
and Undo will crash.

So presumably it's a precondition of editing operations
that CompressRedlines() is a no-op.

Interestingly CompressRedlines() is also called from
SwEditShell::Undo()/Redo().

Ensure it's a no-op later by calling CompressRedlines() immediately
after load.

(Hopefully this should also work for the Insert File case.)

Add a test too.

Change-Id: Iec8135cc60260ed5cfff05a196b5c92cc03265f9
Reviewed-on: https://gerrit.libreoffice.org/49721Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>