RFR: 8322754: click JComboBox when dialog about to close causes IllegalComponentStateException

[Prasanta Sadhukhan]

Clicking to open a JComboBox popup during AWT event processing at the end of which the dialog will be closed causes an IllegalComponentStateException.
Fix is made to check if combobox is showing before showing the popup to prevent the exception.

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Commit messages:
 - fix
 - 8322754: click JComboBox when dialog about to close causes IllegalComponentStateException
 - Merge remote-tracking branch 'upstream/master'
 - Merge remote-tracking branch 'upstream/master'
 - Merge remote-tracking branch 'upstream/master'
 - Merge remote-tracking branch 'upstream/master'
 - Merge
 - Merge branch 'master' of github.com:prsadhuk/jdk
 - Merge remote-tracking branch 'upstream/master'
 - Merge remote-tracking branch 'upstream/master'
 - ... and 2 more: https://git.openjdk.org/jdk/compare/fcf8368e...b50f63c8

Changes: https://git.openjdk.org/jdk/pull/17262/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17262&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322754
  Stats: 94 lines in 2 files changed: 92 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17262.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17262/head:pull/17262

PR: https://git.openjdk.org/jdk/pull/17262