Use qualified std::isnan.

[de-vri-es]

On a recently updated arch system, the kinect2_viewer fails to compile because isnan is not defined in global scope. The header <cmath> defines it in the std namespace [1].

std::isnan is only available since C++11, but if I'm not mistaken the project already requires C++11 so that should not be a problem.

This PR uses the fully qualified name std::isnan to fix the compilation issue.

[1] http://en.cppreference.com/w/cpp/numeric/math/isnan

[kohrt]

Thanks for this PR. That's right, the project needs C++11. But I looked at the code and the isnan is not really needed anyway, because the uint16_t depth value is always a valid number, therefore the float value will never be NAN. I will just remove it from the code.

[de-vri-es]

Ah even better. This can be closed than :)

[kohrt]

fixed with 1a5703b

[de-vri-es]

Awesome, thanks :)