Fix query per vector to not generate an empty retrieve request (#5910)

lib/collection/src/collection/point_ops.rs

@@ -416,6 +416,9 @@ impl Collection {
         timeout: Option<Duration>,
         hw_measurement_acc: HwMeasurementAcc,
     ) -> CollectionResult<Vec<RecordInternal>> {
+        if request.ids.is_empty() {
+            return Ok(Vec::new());
+        }
         let with_payload_interface = request
             .with_payload
             .as_ref()

lib/collection/src/common/fetch_vectors.rs

@@ -224,6 +224,10 @@ impl<'coll_name> ReferencedPoints<'coll_name> {
         let mut collections_names = Vec::new();
         let mut vector_retrieves = Vec::new();
         for (collection_name, reference_vectors_ids) in self.ids_per_collection {
+            // do not fetch vectors if there are no reference vectors
+            if reference_vectors_ids.is_empty() {
+                continue;
+            }
             collections_names.push(collection_name);
             let points: Vec<_> = reference_vectors_ids.into_iter().collect();
             let vector_names: Vec<_> = self