don't send zero-sized binaries to xdcr upr streamer consumer end
don't send zero-sized binaries to xdcr upr streamer consumer end

Because it's useless. And it's not that rare, particularly when full
upr packet is longer than tcp segment.

Change-Id: I2b44a63b488d04da3e74c8d4f81b2f4205d07e76
Reviewed-on: http://review.couchbase.org/35428
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>
Tested-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,daverigby/ns_server,mschoch/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,daverigby/ns_server,nimishzynga/ns_server,membase/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,daverigby/ns_server,daverigby/ns_server,nimishzynga/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,membase/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,membase/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,ceejatec/ns_server