[jdk11u-dev] RFR: 8295289: assert(false) failed: bad AD file

[Martin Doerr]

Trivial and obvious fix for [JDK-8291461](https://bugs.openjdk.org/browse/JDK-8291461). Reproducer passes with this fix.

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Commit messages:
 - 8295289: assert(false) failed: bad AD file

Changes: https://git.openjdk.org/jdk11u-dev/pull/1459/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1459&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295289
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1459.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1459/head:pull/1459

PR: https://git.openjdk.org/jdk11u-dev/pull/1459