Don't throw an error if the user has no username set.
Don't throw an error if the user has no username set.

If the User object with a custom username gets saved, but no username is set an exception is thrown.
This changes checks first if username is not undefined before it calls the toLowerCase method.
saintedlama/passport-local-mongoose,ashertrockman/passport-local-mongoose,traedamatic/passport-local-mongoose,saintedlama/passport-local-mongoose,heitortsergent/passport-local-mongoose-email,theanimal666/passport-local-mongoose,traedamatic/passport-local-mongoose