Group tab is now empty when there are no libraries open (#13473)

* Fix issue #13382, that was probably related to the cleanup logic in GroupTreeViewModel not being triggered properly. Setting the activeDatabase to null when the last LibraryTab is closed seems to fix the issue.

* Update CHANGELOG.md

* Fix title bar DB name and an uncaught exception

- Fixed issue where the database name remained in the title bar after closing all databases.
- Fixed exception triggered by action "Close all" when the welcome tab was open.

---------

Co-authored-by: Christoph <siedlerkiller@gmail.com>

Author: ZodGaz

CHANGELOG.md

@@ -78,6 +78,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 - We fixed an issue where Document Viewer showed technical exceptions when opening entries with non-PDF files. [#13198](https://github.com/JabRef/jabref/issues/13198)
 - When creating a library, if you drag a PDF file containing only a single column, the dialog will now automatically close. [#13262](https://github.com/JabRef/jabref/issues/13262)
 - We fixed an issue where the tab showing the fulltext search results would appear blank after switching library. [#13241](https://github.com/JabRef/jabref/issues/13241)
+- We fixed an issue where the groups were still displayed after closing all libraries. [#13382](https://github.com/JabRef/jabref/issues/13382)
 - Enhanced field selection logic in the Merge Entries dialog when fetching from DOI to prefer valid years and entry types. [#12549](https://github.com/JabRef/jabref/issues/12549)
 
 ### Removed

jabgui/src/main/java/org/jabref/gui/frame/JabRefFrame.java

@@ -419,7 +419,6 @@ private void initBindings() {
                                                   .noneMatch(ltab -> ((LibraryTab) ltab).getBibDatabaseContext().getUid().equals(activeUID));
                     if (wasClosed) {
                         tabbedPane.getSelectionModel().selectNext();
-                        return;
                     }
                 }
 
@@ -595,6 +594,10 @@ public boolean closeTabs(@NonNull List<LibraryTab> tabs) {
             // Trigger org.jabref.gui.LibraryTab.onClosed
             Event.fireEvent(libraryTab, new Event(this, libraryTab, Tab.CLOSED_EVENT));
         }
+        // Force group update in the GroupTreeViewModel when all the libraries are closed
+        if (tabbedPane.getTabs().isEmpty()) {
+            stateManager.setActiveDatabase(null);
+        }
         return true;
     }
 
@@ -722,6 +725,7 @@ private class CloseAllDatabaseAction extends SimpleCommand {
 
         @Override
         public void execute() {
+            tabbedPane.getTabs().removeIf(t -> t instanceof WelcomeTab);
             for (Tab tab : tabbedPane.getTabs()) {
                 Platform.runLater(() -> closeTab((LibraryTab) tab));
             }