fix sampler for nearest neighbor scaling

[CrystalP]

Fixes the setup of a sampler with point sampling. To be merged with the original commit 7242d4a2e333a2d65cb8acb67ed685f3fd6a4870

Initialization of m_pSampNearestNeightbor in constructor is not needed (not a base type), but it follows the pattern of the rest of the code.

Screenshots (if appropriate):

[garbear]

I tested and it works. Thanks!!!