[OpenJDK 2D-Dev] RFR: 8267116: Lanai: Incorrect AlphaComposite for VolatileImage graphics

[Alexey Ushakov]

Added one more bit for subIndex

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Commit messages:
 - 8267116: Lanai: Incorrect AlphaComposite for VolatileImage graphics

Changes: https://git.openjdk.java.net/jdk/pull/4018/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4018&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267116
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4018.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4018/head:pull/4018

PR: https://git.openjdk.java.net/jdk/pull/4018