RFR: 8284400: Improve XPath exception handling [v2]

[Joe Wang]

> Addresses an insufficiency of error handling in the XPath implementation. Some cleanup where appropriate, without attempting to do too much as this is a component that hasn't had much changes for 15 years, a fairly stable application.
> 
> Test: tier2 passed
> JCK: JCK XML tests passed

Joe Wang has updated the pull request incrementally with one additional commit since the last revision:

  update copyright year and LastModified tag

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8910/files
  - new: https://git.openjdk.java.net/jdk/pull/8910/files/a03cb0d4..12575c95

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8910&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8910&range=00-01

  Stats: 4 lines in 3 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8910.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8910/head:pull/8910

PR: https://git.openjdk.java.net/jdk/pull/8910