Fix livelocking in peerDigestHandleReply (#698)

Fix livelocking in peerDigestHandleReply (#698)

peerDigestHandleReply() was missing a premature EOF check. The existing
peerDigestFetchedEnough() cannot detect EOF because it does not have
access to receivedData.length used to indicate the EOF condition. We did
not adjust peerDigestFetchedEnough() because it is abused to check both
post-I/O state and the state after each digest processing step. The
latter invocations lack access to receivedData.length and should not
really bother with EOF anyway.