BUG: boundary data sampling is incorrect when no fields are sampled

Cross reference: EP#1606

When no fields are sampled, the boundary data exports points of faces instead of face center.

added bug label

mentioned in commit 7f2cbd6c

@Prashant - pushed a single commit to fix-2163-boundaryData for testing (one commit on top of master). Please check and report go/no-go here, will merge to master after that.

assigned to @mark

Looks good. Please push.

closed via commit 7f2cbd6c

mentioned in commit e95f8b1a

mentioned in commit d9bc7c09