Add guard to impl of Enumerable for Function
Add guard to impl of Enumerable for Function

This improves the stacktrace in case of wrong dispatch.

ggcampinho/elixir,ggcampinho/elixir,antipax/elixir,gfvcastro/elixir,pedrosnk/elixir,kimshrier/elixir,michalmuskala/elixir,gfvcastro/elixir,antipax/elixir,lexmag/elixir,kelvinst/elixir,elixir-lang/elixir,lexmag/elixir,beedub/elixir,kelvinst/elixir,kimshrier/elixir,pedrosnk/elixir,beedub/elixir,joshprice/elixir