JSCBC-828: Fixed view-query 0 limit queries.
JSCBC-828: Fixed view-query 0 limit queries.

Motivation
----------
Executing a view query with a limit of 0 is a valid use-case
but we previously elided the limit value if it was 0.

Changes
-------
Modified the check for limit to check for undefined rather
than using a falsey check.

Change-Id: I94f9e7af78d68ff54f0c958d5971602a4f7880b5
Reviewed-on: http://review.couchbase.org/c/couchnode/+/143317
Reviewed-by: Charles Dixon <e13bf4498b4994e133fd3586350658dc4a59329a@gmail.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

brett19/couchnode,couchbase/couchnode,couchbase/couchnode,brett19/couchnode,brett19/couchnode,couchbase/couchnode,couchbase/couchnode