fix: failed to sync work when binding's target clusters are empty

[vie-serendipity]

What type of PR is this?

/kind bug
What this PR does / why we need it:
For now, when binding is not scheduled, which means clusters field is empty, work will still be synced. And this log will be printed.
Sync work of resourceBinding(%s/%s) successful
But actually no work is created. I think it's necessary to check whether clusters field of binding is empty. I'not sure this should be added to predicates of controller or just put it into syncbinding function, like my current pr code. I think the latter is better, in this way, users can see scheduling encounter some problems.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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[XiShanYongYe-Chang]

Hi @vie-serendipity thanks for your feedback. We can really decide whether to reconcile the ResourceBinding based on whether the scheduling has been completed (the ClusterResourceBinding has the same processing logic), which can save some unnecessary tuning. Therefore, I understand that this should be an optimization, not a bug fix.

In addition, we can judge whether the scheduling is completed in this way: obj.Status.SchedulerObservedGeneration == obj.Generation, this can cover the situation where there is no scheduling result.