InputStreamImpl::ReadBlockContinuation stores wrong pointers of buffers

Somewhere between InputStream->PositionRead and the asio code the pointer to the destination buffer gets lost. PositionRead will correctly return the number of bytes read but the buffer won't be filled.

This only seems to effect the remote_block_reader, RPC calls are working.

Valgrind error:
Syscall param recvmsg(msg.msg_iov) points to uninitialised byte(s)

msg.msg_iov[0] should equal the buffer pointer passed to PositionRead

Hit when using a promise to make the async call block until completion.

auto stat = std::make_shared<std::promise<Status>>();
std::future<Status> future(stat->get_future());

size_t readCount = 0;
auto h = [stat, &readCount,buf](const Status &s, size_t bytes) {
stat->set_value(s);
readCount = bytes;
};

char buf[50];
inputStream->PositionRead(buf, 50, 0, h);

//wait for async to finish
future.get();