Fix generate bibtex key overwrite warning dialog

[Siedlerchr]

Fixes #4417

The problem was that the GenerateBibtexKeyAction is executed using a TaskExecutor and therefore not run on the FX Thread. Unfortunately the exception was swallowed and not reported.

---

• Change in CHANGELOG.md described
• Tests created for changes
• Manually tested changed features in running JabRef
• Screenshots added in PR description (for bigger UI changes)
• Ensured that the git commit message is a good one
• Check documentation status (Issue created for outdated help page at help.jabref.org?)

[tobiasdiez]

Although this works, can please instead rework the TaskExecutor code using JavaFX tasks. I think, we are at a point where we can try to trough out swing instead of inserting runInJavaFXThread everywhere.

[Siedlerchr]

Well, it is already using the BackgroundTask.wrap to create a background thread, which has nothing to do with the swing stuff:

     BackgroundTask.wrap(this::generateKeys)
                      .executeWith(Globals.TASK_EXECUTOR);

Which of course creates a pool thread. I see no other way to show a dialog

[tobiasdiez]

Just put the start of the generateKeys method that is related to the key overwrite dialog before the Background.wrap() statement. Anything in wrap should perform an action and only code in success or failure should be allowed to interact with the user.