r23057: only call the async recv function for the first pending receive, not

r23057: only call the async recv function for the first pending receive, not
all pending receives, when the transport dies. This is because the
async callback most commonly shuts down the connection (it's the only
reasonable thing to do when it's dead), and that frees the whole
context. That means that if we loop more than once, we'll end up using
freed memory.
(This used to be commit 75d537d3a5e3fc5258ce48bfec0c0ce6160978f6)