Add null check for the Aqua LnF situation when tab is hidden die to the tabs overflow.
------------- Commit messages: - 8322239: [macos] a11y : java.lang.NullPointerException is thrown when focus is moved on the JTabbedPane Changes: https://git.openjdk.org/jdk/pull/17736/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17736&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8322239 Stats: 6 lines in 1 file changed: 3 ins; 0 del; 3 mod Patch: https://git.openjdk.org/jdk/pull/17736.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/17736/head:pull/17736 PR: https://git.openjdk.org/jdk/pull/17736
