Previously, currPos, obtained using notifier.CurrentPosition(), is passed
to GetNotifyChannel. Since this is already the latest position on the
server, the client won't get updates until (1) a even newer event arrives at
the server, or (2) the /sync request times out.
(2) above is possible because when it times out, notifier calculates
currentSyncForUser based on syncReq, which contains the correct since pos
token that the client sent the server.
Signed-off-by: Alex Chen <minecnly@gmail.com>