8340554: Improve MessageFormat readObject checks

[justin-curtis-lu]

Please review this PR which improves the readObject logic for j.text.MessageFormat.

No offset should be larger than the pattern length. We already ensure the offsets when consumed backwards are equal/descending. The existing first/initial check was off by 1 since it was checking against the pattern length + 1; (see L2040 and L2043).

Please see the JBS issue for further info and other test details.

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Progress

• [x] Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• [x] Change must not contain extraneous whitespace
• [x] Commit message must refer to an issue

Issue

• JDK-8340554: Improve MessageFormat readObject checks (Bug - P4)

Reviewers

• Naoto Sato (@naotoj - Reviewer)

Reviewing

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