COMP: Fix BSplineDeformableTransformTest for GCC4.8.2.

When build with -O3, GCC 4.8.2, the BSplineDeformableTransformTest
was segfaulting in subtest itkBSplineDeformableTransformTest2.

The error occurs in UpdateValueGridRegion().  An apparent optimization
bug is worked around by changing how size and index are initialized.

UpdateValidGridRegion is also no longer called in the contructor as the
computation results in an invalid computation of m_ValidRegionLast.

Change-Id: I1447578679b4d146102011fb72e776b313b89793
Merge topic 'gcc4.8.2-BSplineDeformable'

1b8974e COMP: Fix BSplineDeformableTransformTest for GCC4.8.2.