RFR: 8314274: G1: Fix -Wconversion warnings around G1CardSetArray::_data [v2]

[Thomas Schatzl]

On Wed, 16 Aug 2023 09:26:32 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Add value-range check and explicit type conversion. The second write has its check at the beginning of the method, so doesn't require an assertion.
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/15289#pullrequestreview-1580680663