RFR: 8267860: Off-by-one bug when searching arrays in AlpnGreaseTest

[Kevin Driver]

This PR resolves: https://bugs.openjdk.org/browse/JDK-8267860

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

Commit messages:
 - Update AlpnGreaseTest.java
 - JDK-8267860: off-by-one error

Changes: https://git.openjdk.org/jdk/pull/9131/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8267860
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9131.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9131/head:pull/9131

PR: https://git.openjdk.org/jdk/pull/9131