PYCBC-236: Handle row population outside of _fetch()

Change-Id: Ic9aaace50309a198cfb37dca263ee39b453ea01c
Reviewed-on: http://review.couchbase.org/34249
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Volker Mische <volker.mische@gmail.com>