fix ClassCastException during drag-and-drop caused by transient tab state

[070jhz]

Closes #12921

the type-check predicate can behave inconsistently during the interaction, likely a timing/synchronization issue caused by how the UI updates the tab list during drag-and-drop while the filtered list is reacting to changes.
directly mapping over the original tabs list with a lambda that accoutns for possible non-LibraryTab entries solves the issue. this results in openDatabaseList possibly holding null values but since it is a private member not accessed elsewhere and we bind a filtered version to StateManager::openDatabases, it should not cause any further bugs.

a more robust solution could be implemented with listeners, but it might be overkill ?

Steps to test

1. Disable the setting to "Hide Tab bar when single library is present"
2. Create a library (Or create 2 if you skipped step 1)
3. Click and drag the Welcome tab and move it beside the newly created library
4. Exception no longer occurs

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [/] Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• [/] Screenshots added in PR description (if change is visible to the user)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

This is a JavaFX issue. @Siedlerchr how to report?

Update: Moved to #12921 (comment) as it concerns more the original issue than this work around

[koppor]

Code nees to be adapted, since the FilteredList is not right at all due to a JavaFX bug.

[koppor]

I think, the list will be wrong on tab change. Maybe some custom code needs to be placed here? IDK.

[070jhz]

is there a specific case you had in mind ? i manually tested tab changes (opening, closing, rearranging) and openDatabaseList seems to accurately reflect the tab state.

[Siedlerchr]

you can file a bug report https://bugreport.java.com/bugreport/
It will take a while until it is processed
For company you can use JabRef e.V.

[koppor]

you can file a bug report bugreport.java.com/bugreport

Submitted a JavaFX error report - internal review ID : 9078592

[070jhz]

Code nees to be adapted, since the FilteredList is not right at all due to a JavaFX bug.

exception no longer occurs with no FilteredList usage, with the lists accurately reflecting the state of the tabs. i added some listener code to filter out the nulls from the mapping and keep it in sync with stateManager::openDatabaseList

[koppor]

Some code simplificatoin comments.

[trag-bot]

@trag-bot didn't find any issues in the code! ✅✨