Add panic recovery if typecast fails in IsNotFoundError
Add panic recovery if typecast fails in IsNotFoundError

Change-Id: I3d31837b276c3a5c57d16aefceb2da5b22fa255f
Reviewed-on: http://review.couchbase.org/49858
Reviewed-by: Manik Taneja <ab0e3979665ad7ee15da870324c623916e4596d3@couchbase.com>
Tested-by: Manik Taneja <ab0e3979665ad7ee15da870324c623916e4596d3@couchbase.com>

nimishzynga/go-couchbase,couchbase/go-couchbase