Fix incr handling for empty key (#2540)
Fix incr handling for empty key (#2540)

On an empty key, incr was returning error instead of '0' after singleOps refactoring
tophatch/sync_gateway,couchbaselabs/sync_gateway,couchbaselabs/sync_gateway,tophatch/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway,couchbaselabs/sync_gateway,tophatch/sync_gateway