Foam::eigenValues fails for algebraic multiplicity > 1

When a patch is axi-symmetric its moment of inertia tensor has two identical eigenvalues.

In this situation Foam::eigenValues returns two zeros instead of the actual eigenvalues.

The attached case demonstrates this. Run the Allrun script and have a look in log.surfaceInertia: bug-fix-surfaceInertia.tar.gz

I fixed this problem in this branch: https://develop.openfoam.com/Development/OpenFOAM-plus/tree/bug-fix-eigneValuesForSymTensorsAndSurfInertiaForAxisymShapes