Fix recent bug with trilinic 1D DD

A recent bug-fix (c8d919a3) for triclinic 1D domain decompostion
introduced a bug for boxes with box[YY][XX]!=0.
Fixes #1656.
Refs #1631.

Change-Id: I06b9376212390b73e90a3ce9704dee2bad9693fb
Merge release-4-6 into release-5-0

Change-Id: I952a9b8dd61c0eb7456c640997093a1a5fea8fc3
Merge "Merge release-4-6 into release-5-0" into release-5-0