<AWT Dev> RFR: 8259729: Missed JNFInstanceOf -> IsInstanceOf conversion

[Phil Race]

One line fix of a missed update

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Commit messages:
 - 8259729: Missed JNFInstanceOf -> IsInstanceOf conversion

Changes: https://git.openjdk.java.net/jdk/pull/2066/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2066&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259729
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2066.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2066/head:pull/2066

PR: https://git.openjdk.java.net/jdk/pull/2066