Add check for if num_items_in_batch is not None

[muellerzr]

What does this PR do?

Adds a check before calling .gather() to make sure that num_items_in_batch actually has a value

Fixes #35076

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@Rocketknight1 @SunMarc

[SunMarc]

Thanks for the PR ! LGTM !

[HuggingFaceDocBuilderDev]

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[Rocketknight1]

I give this my Small Enough To Not Require A Real Core Maintainer stamp of approval 🕹️

[ving666]

@Rocketknight1 @SunMarc We encountered the same issue. When will this MR be merged? Thank you！

[SunMarc]

I'll let @muellerzr decide either to merge this one or this PR : #35399

[muellerzr]

Thanks! This one got swept under (not good)