BUG #14099. Fixes spreadsheet selections with composite datasets.

vtkMarkSelectedRows was not marking rows selected correctly for composite
datasets. During the refactoring for commit c33bc2b1, we lost  the handling of
composite data selections. This fixes that issue.

Change-Id: I7a2e9ce1a3c52425ce616f426ae044f32a75de34
Merge topic '14099_spreadsheet_selection' into next

e07440f BUG #14099. Fixes spreadsheet selections with composite datasets.