Segment Replication stats throwing NPE when shards are unassigned or …

…are in delayed allocation phase

Signed-off-by: Rampreeth Ethiraj <ethirajrampreeth@gmail.com>

server/src/main/java/org/opensearch/index/seqno/ReplicationTracker.java

@@ -1254,6 +1254,7 @@ public ReplicationCheckpoint getLatestReplicationCheckpoint() {
     private boolean isPrimaryRelocation(String allocationId) {
         Optional<ShardRouting> shardRouting = routingTable.shards()
             .stream()
+            .filter(routing -> Objects.nonNull(routing.allocationId().getId()))
             .filter(routing -> routing.allocationId().getId().equals(allocationId))
             .findAny();
         return shardRouting.isPresent() && shardRouting.get().primary();