Fix check_nan to use the scal version so rev/core/ddv_vari_test does not break
Fix check_nan to use the scal version so rev/core/ddv_vari_test does not break

stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math