[jdk11u-dev] RFR: 8318951: Additional negative value check in JPEG decoding

[Amos Shi]

Backport of [JDK-8318951](https://bugs.openjdk.org/browse/JDK-8318951)
- Clean Backport

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Commit messages:
 - Backport 75ce02fe74e1232bfa8d72b4fdad82ed938ef957

Changes: https://git.openjdk.org/jdk11u-dev/pull/2372/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2372&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318951
  Stats: 8 lines in 2 files changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2372.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2372/head:pull/2372

PR: https://git.openjdk.org/jdk11u-dev/pull/2372