Fix a problem to inicializate spatial_data

[mgesto]

No description provided.

[taketwo]

There is a special syntax to zero-initialize an array allocated with new, see here.

In our case it would be as simple as:

kiss_fft_scalar * spatial_data = new kiss_fft_scalar[nbins]();

Please also change the comment above to explain what's going on, because this is not a very well-known feature of C++ and as such may be confusing for those who read the code.

[mgesto]

Ok, thanks, now is changued, maybe you can improve the coment above.