Async parsing accepts weird stuff

[travisbrown]

Noted by @BenFradet here. Might be #135?

scala> import org.typelevel.jawn.{AsyncParser, NullFacade}
import org.typelevel.jawn.{AsyncParser, NullFacade}

scala> val p = AsyncParser[Unit](AsyncParser.UnwrapArray)
p: org.typelevel.jawn.AsyncParser[Unit] = org.typelevel.jawn.AsyncParser@3b623061

scala> p.absorb("}")(NullFacade)
res0: Either[org.typelevel.jawn.ParseException,Seq[Unit]] = Right(ArrayBuffer())

In 0.13.0 you get an error:

scala> p.absorb("}")(NullFacade)
res0: Either[jawn.ParseException,Seq[Unit]] = Left(jawn.ParseException: expected json value got } (line 1, column 1))

(Both 0.13.0 and 0.14.0 fail with the same error on finish.)