CIE 1994 colour difference implementation might generate NaN values.

[pfk-beta]

I do not have certain pixel for reproducing error, but according to http://brucelindbloom.com/index.html?Eqn_DeltaE_CIE94.html footnotes it is possible. I would like to report it, and solve pull request.

[KelSolaar]

Hi @pfk-beta!

Thanks for reporting this! I think it would be great to identify which cases are generating NaNs first. I'll continue the discussion in #539! See you there :)

Cheers,

Thomas