[jdk8u-dev] RFR: JDK-8324530: Build error with gcc 10

[Thomas Stuefe]

This is a trivial fix to a build error (and the underlying off-by-one error, which is only theoretical) gcc 10 warns about.

Note that this issue has been fixed in JDK 11 and later as part of 8140594: "Various minor code improvements (compiler)", but that patch is much larger and would need more intense review. Here, I'd like to just fix this one problem that breaks the build with gcc 10.

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Commit messages:
 - fix off by one

Changes: https://git.openjdk.org/jdk8u-dev/pull/424/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=424&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324530
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/424.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/424/head:pull/424

PR: https://git.openjdk.org/jdk8u-dev/pull/424