Exception if .learn is malformed

[sammarcus]

If a particular lab happens to have a .learn file that has no contents, it errors here with the .any:

learn-open/lib/learn_open/lessons/ios_lesson.rb

Line 6 in 2f22431

(languages & ["swift", "objc"]).any?

If there isn't a default language being inserted into languages array this may be why, will explore a fix later this week -- (unless this is desired behavior as we consider a proper .learn bare minimum?)

[sammarcus]

cc @StevenNunez saw you had worked on this recently 👀