[jdk15u-dev] RFR: 8297530: java.lang.IllegalArgumentException: Negative length on strings concatenation

[Yuri Nesterenko]

backporting because the issue exists here as well.
Clean backports, expected test behavior, tier1 OK.

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Commit messages:
 - Backport 87d1097d9be1ef804bfd4640a4254126242b1d8c

Changes: https://git.openjdk.org/jdk15u-dev/pull/314/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk15u-dev&pr=314&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297530
  Stats: 141 lines in 2 files changed: 139 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk15u-dev/pull/314.diff
  Fetch: git fetch https://git.openjdk.org/jdk15u-dev pull/314/head:pull/314

PR: https://git.openjdk.org/jdk15u-dev/pull/314