RFR: 8322239: [macos] a11y : java.lang.NullPointerException is thrown when focus is moved on the JTabbedPane [v5]

[Alexander Zuev]

> Add null check for the Aqua LnF situation when tab is hidden die to the tabs overflow.

Alexander Zuev has updated the pull request incrementally with two additional commits since the last revision:

 - added space to a catch clause
 - Moved frame disposal to the separate method to make it more thread safe

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/17736/files
  - new: https://git.openjdk.org/jdk/pull/17736/files/aa380530..d12edf04

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17736&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17736&range=03-04

  Stats: 16 lines in 1 file changed: 7 ins; 5 del; 4 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