util: Fix call_all hang when stream is pending

[leoyvens]

Currently call_all will hang in a busy loop if called when the input stream is pending.

[hawkw]

this looks good to me overall, thanks for the fix!

i commented on one style suggestion, but it's not a blocker.

[hawkw]

nit, take it or leave it: now that we return Poll::Pending in this case, we could simplify the nested match to just a single match by using ready! instead:

            // If it is, gather the next request (if there is one), or return `Pending` if the
            // stream is not ready.
            // TODO: We probably want to "release" the slot we reserved in Svc if the
            // stream returns `Pending`. It may be a while until we get around to actually
            // using it.
            match ready!(this.stream.as_mut().poll_next(cx)) {
                Some(req) => {
                    this.queue.push(svc.call(req));
                }
                None => {
                    // We're all done once any outstanding requests have completed
                    *this.eof = true;
                }
            }

[leoyvens]

Thank you for the review, I've done this refactor.

[hawkw]

looks great, thank you!

[leoyvens]

@hawkw Thanks for the review! I forced push so this still needs a merge.