[client] Improve initialization of Cluster class (#292)

Author: WangS-C

fluss-common/src/main/java/com/alibaba/fluss/cluster/Cluster.java

@@ -83,22 +83,17 @@ public Cluster(
             List<BucketLocation> bucketsForTable = entry.getValue();
             // Optimise for the common case where all buckets are available.
             boolean foundUnavailableBucket = false;
+            List<BucketLocation> availableBucketsForTable = new ArrayList<>(bucketsForTable.size());
             for (BucketLocation bucketLocation : bucketsForTable) {
                 if (bucketLocation.getLeader() != null) {
                     tmpAvailableLocationByBucket.put(
                             bucketLocation.getTableBucket(), bucketLocation);
+                    availableBucketsForTable.add(bucketLocation);
                 } else {
                     foundUnavailableBucket = true;
                 }
             }
             if (foundUnavailableBucket) {
-                List<BucketLocation> availableBucketsForTable =
-                        new ArrayList<>(bucketsForTable.size());
-                for (BucketLocation loc : bucketsForTable) {
-                    if (loc.getLeader() != null) {
-                        availableBucketsForTable.add(loc);
-                    }
-                }
                 tmpAvailableLocationsByPath.put(
                         physicalTablePath, Collections.unmodifiableList(availableBucketsForTable));
             } else {