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

[Albert Mingkun Yang]

> 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

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15289/files
  - new: https://git.openjdk.org/jdk/pull/15289/files/c6493f25..073f9cbe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15289&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15289&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15289.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15289/head:pull/15289

PR: https://git.openjdk.org/jdk/pull/15289