Fix bootstrap without known validators (backport #25293) (#25318)

* fix bootstrap without known validators (#25293)

(cherry picked from commit 2412276)

# Conflicts:
#	validator/src/bootstrap.rs

* pr: fix merge conflicts

* pr: checks

Co-authored-by: DimAn <diman@diman.io>
Co-authored-by: Brooks Prumo <brooks@solana.com>

validator/src/bootstrap.rs

@@ -1107,19 +1107,20 @@ mod with_incremental_snapshots {
         bootstrap_config: &RpcBootstrapConfig,
         rpc_peers: &[ContactInfo],
     ) -> Vec<PeerSnapshotHash> {
-        let known_snapshot_hashes =
-            get_snapshot_hashes_from_known_validators(cluster_info, validator_config);
-
         let mut peer_snapshot_hashes = get_eligible_peer_snapshot_hashes(
             cluster_info,
             validator_config,
             bootstrap_config,
             rpc_peers,
         );
-        retain_peer_snapshot_hashes_that_match_known_snapshot_hashes(
-            &known_snapshot_hashes,
-            &mut peer_snapshot_hashes,
-        );
+        if validator_config.known_validators.is_some() {
+            let known_snapshot_hashes =
+                get_snapshot_hashes_from_known_validators(cluster_info, validator_config);
+            retain_peer_snapshot_hashes_that_match_known_snapshot_hashes(
+                &known_snapshot_hashes,
+                &mut peer_snapshot_hashes,
+            );
+        }
         retain_peer_snapshot_hashes_with_highest_full_snapshot_slot(&mut peer_snapshot_hashes);
         retain_peer_snapshot_hashes_with_highest_incremental_snapshot_slot(
             &mut peer_snapshot_hashes,