Merge topic 'plot3d-error-handling-fix'

d91ecf98 BUG: Was using the wrong extent in computation.
005e70d3 Fixed warnings.
5f15c59d Cleaned up error handling in plot3d reader.

Acked-by: Kitware Robot <kwrobot@kitware.com>
Reviewed-by: Utkarsh Ayachit <utkarsh.ayachit@kitware.com>
Merge-request: !433