RFR: JDK-8312453: GrowableArray should assert for length overflow on append

[Thomas Stuefe]

Trivial change to assert that we don't overflow on append.

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Commit messages:
 - JDK-8312453-GrowableArray-should-assert-for-length-overflow-on-append

Changes: https://git.openjdk.org/jdk/pull/14951/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14951&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312453
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14951.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14951/head:pull/14951

PR: https://git.openjdk.org/jdk/pull/14951