`body::stream` too existential to find itself

Version 0.4.3

Platform n/a

Description because body::stream returns an existential type to encapsulate http-body-util's BodyDataStream the concrete type seems not to infer when monomorphizing a subsequent closure

reproduction:

warp::body::stream().map(|bs| {
  bs.map(|_| 0u8);
  warp::reply()
})