Fix issues with OpenEXR images with more channels than RGB

[Latios96]

This PR fixes issue #30

To me it seems like numRecognizedChannels and exrHeader.num_channels were confused. Using numRecognizedChannels instead of exrHeader.num_channels seems more appropriate when loading the data, since the OpenEXR image can contain an arbitrary amount of (unused) channels.

I don't know if this is the best fix, but it worked for me.

[inversepixel]

Thanks so much! This is really how the code should have worked... this is the first time I encounter EXR images with more channels, so the code has never really been tested.
Anyway, I removed some of the previous warnings and minor cleanup as well. You can see here, if you are interested:
de24b93

[Latios96]

Your welcome, great it is fixed and simplified now!