Fix vtkCompositePainter with vtkMultiPieceDataSet

This fixes a bug in the vtkCompositePainter class when using
the new composite data set attributes with multi-piece data sets.

Change-Id: I447a69b46d4d234046a6f6e007500d2b23001c04
Merge topic 'fix-composite-painter-with-multi-piece' into master

7509a7f8 Fix vtkCompositePainter with vtkMultiPieceDataSet