23234fa14f
Because `self.pending` doesn't necessarily get cleaned up in a timely fashion - rather, only when the user calls `poll_ready()` - it was possible for it to refer to a stream that has already been closed. This would lead to a panic the next time that `poll_ready()` was called. Instead, use an `OpaqueStreamRef`, bumping the refcount. A change to an existing test is included which demonstrates the issue.