xmerge: Unused assignment

Change-Id: Ie059c6689976c0a52fedaa6fdee2dd36d944eb56
Reviewed-on: https://gerrit.libreoffice.org/10574
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>