MB-18887 fix panic in GetVBMap
MB-18887 fix panic in GetVBMap

Change-Id: Ifdcde33d753b49342761cba86a78de14363483dc
Reviewed-on: http://review.couchbase.org/62196
Reviewed-by: Ritesh Motlani <b60f10fec4d5a51ec022ce7ab6b20e38bf35cc58@couchbase.com>
Reviewed-by: Sitaram Vemulapalli <8d86a491dcdf321bac78bef141a8229a59bf9211@couchbase.com>
Tested-by: Yu Sui <441df8f56b0013c208d96c9ec8bc5fdb2106e456@gmail.com>
Reviewed-on: http://review.couchbase.org/62206
Reviewed-by: Yu Sui <441df8f56b0013c208d96c9ec8bc5fdb2106e456@gmail.com>

couchbase/go-couchbase