GPU Calc: fix regression caused by recent isValid() change

Change-Id: I885a222bf8a7ca4275867585ccf067a1ba7822c7
GPU Calc: fix compilation failure on Windows due to missing NAN macro

Change-Id: I0d53dcf147a06f831120c5489b2975e42ea6120b
GPU Calc: fix typo in NAN macro

Change-Id: I34299e0fc692c2ab43fe0c1fffaada348742d19f