DefaultExecutionGraphBuilder#isCheckpointingEnabled may return Wrong Value when checkpoint disabled

The DefaultExecutionGraphBuilder will call 
isCheckpointingEnabled(JobGraph jobGraph)
to determine whether the job has enabled Checkpoint and whether to initialize CheckpointCoordinator related components such as CheckpointCoordinator, CheckpointIDCounter , etc.

// DefaultExecutionGraphBuilder#isCheckpointingEnabled

public static boolean isCheckpointingEnabled(JobGraph jobGraph) {
    return jobGraph.isCheckpointingEnabled();
}

The problem is that the logic for determining isCheckpointingEnable here is inaccurate, as jobGraph. getCheckpointingSettings() will not be NULL when checkpoint is not enabled, but with CheckpointCoordinatorConfiguration.DISABLED_CHECKPOINT_INTERVAL Interval

// JobGraph#isCheckpointingEnabled

public boolean isCheckpointingEnabled() {

    if (snapshotSettings == null) {
        return false;
    }

    return snapshotSettings.getCheckpointCoordinatorConfiguration().isCheckpointingEnabled();
} 

The method to fix this problem is also quite clear. We need to directly reuse the result of jobGraph.isCheckpointingEnable() here