Make sure that current database is "shared"

[Gena928]

Fixes #6959
JabRef always tries to pull changes from shared database, even if current database is not shared.
Added filter to ensure that current db is shared.

• Change in CHANGELOG.md described (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[koppor]

The original issue did not provide a screenshot. I guess that "Pull changes from database" is enabled even if there isn't a shared database. Thus, the solution is NOT to fix the action pulling the changes, but to fix the menu entry being enabled only for shared datbases.

Related: koppor#419

[Gena928]

@koppor ,
thanks for a comment. Indeed, now I see that filtering DB type is ugly solution. I'll try to make a new one.

[Siedlerchr]

The idea is not bad, just at the wrong position.
The solution would be to create another BooleanExpression in the ActionHelper class, e..g needsSharedDatabase
filter there
And in the action you can then bind it, e..g:
this.executable.bind(ActionHelper.needsEntriesSelected(stateManager));