Fix `std::min` comparison on i686
Fix `std::min` comparison on i686

Summary: Explicitly cast the second argument to unsigned, since otherwise, on `i686` it is inferred to be an `int64_t` instead and the comparison failed.

Reviewed By: yfeldblum

Differential Revision: D30050062

fbshipit-source-id: b46589d1d7cac93c42baa9a8e1dc846a780ecfb5

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