Possible bugfix for LMM fit outputting NAs for all comparisons

[lmweber]

See https://github.com/SamGG/diffcyt commits and email discussion

[LukaTandaric]

@lmweber I'm sorry, but I cannot find anything about the LMM bugfix in the commits of the repository you linked to. Could you please assist me in my search? Thanks.

[SamGG]

Hi guys,
Sorry I deleted my repo in order to fork from here, and then to reinsert and validate my patch before sending a PR.
It should be ready on Monday.
Best,
Samuel