FindDescriptor with blob=True does not work without k_neighbors

Is that intentional?

Server logs:
```
"[
   {
      ""entities"" : [
         {
            ""VD:descSetPath"" : ""db/descriptors/020419_inception_v3_64emb"",
            ""VD:dimensions"" : 64
         }
      ],
      ""returned"" : 1,
      ""status"" : 0
   },
   {
      ""info"" : ""Unknown operation type for query\n"",
      ""status"" : -1
   }
]"
```