Fix and extend AffineMap3DTest

Commit fixes two issues with the test
* WALBERLA_CHECK_FLOAT_EQUAL in checkVolume was commented out, so we
  did in fact check nothing.
* std::array volume was too short by one; did only cause a problem
  after added a new test.
We extend the test to also check that AffineMap3D::evalFinv() work
and make the test run faster by reducing the grid level for the
existing test.