RFR: 8284548: Invalid XPath expression causes StringIndexOutOfBoundsException

[Joe Wang]

Patch note:

    A previous patch had a bug that missed the boundary check, that will cause StringIndexOutOfBoundsException to be thrown instead of XPathExpressionException as expected.
    
Fix: the fix is to check the boundaries of the parameter "index". Objects.checkIndex is removed as it's redundant.

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Commit messages:
 - 8284548: Invalid XPath expression causes StringIndexOutOfBoundsException

Changes: https://git.openjdk.java.net/jdk/pull/8323/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8323&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284548
  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8323.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8323/head:pull/8323

PR: https://git.openjdk.java.net/jdk/pull/8323