enumJsonFormat works on datatypes with non-nullary constructors

[dfithian]

From ConferOpenSource/composite#57

And this means it'll enumerate many more possible values then it should:

Composite.Aeson VitalPrelude ABE> data Foo2 = Foo | Bar Word8 deriving (Eq, Ord, Generic, Show)
Composite.Aeson VitalPrelude ABE> let ejf2 = enumJsonFormat "" :: JsonFormat () Foo2
Composite.Aeson VitalPrelude ABE> ABE.parseValue (fromJsonWithFormat ejf2) (Data.Aeson.String "Foox")
Left (BadSchema [] (FromAeson "expected one of Foo, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar,
 Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar,
Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, B
ar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Ba
r, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar
, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar,
 Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar,
Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, B
ar, not Foox"))