RFR: 8290488: IBM864 character encoding implementation bug

[Naoto Sato]

Adding an extra c2b mapping for the `%` in `IBM864` charset. The discrepancy came from the mapping difference between MS and IBM.

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Commit messages:
 - Fix 0x25 c2b in IBM864

Changes: https://git.openjdk.org/jdk/pull/9661/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9661&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290488
  Stats: 6 lines in 3 files changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/9661.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9661/head:pull/9661

PR: https://git.openjdk.org/jdk/pull/9661