fix: Fix duplicate enqueue item problem in bloom download queue when do sync download

[honganan]

A missing return will cause item enqueued twice in sync download scenario. That cause the response not like expected.

Suppose we want to fetch a blocks array: [0, 1, 2]. Enqueued items are [0, 0, 1, 1, 2, 2]，If we want response sorted we wait 3 times response will get [0, 0, 1]

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Which issue(s) this PR fixes:
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[chaudum]

Great find. Thanks for fixing!