RFR: JDK-8288692: jdk/javadoc/doclet/testTagMisuse/TestTagMisuse.java fails after JDK-8288545

[Jonathan Gibbons]

Please review a simple fix to address an NPE that can occur with a bad (empty) `{@link}` tag.

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Commit messages:
 - JDK-8288692: jdk/javadoc/doclet/testTagMisuse/TestTagMisuse.java fails after JDK-8288545

Changes: https://git.openjdk.org/jdk19/pull/37/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk19&pr=37&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288692
  Stats: 9 lines in 3 files changed: 8 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk19/pull/37.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/37/head:pull/37

PR: https://git.openjdk.org/jdk19/pull/37