Fix the Fix > Close All action not resulting in the welcome screen being shown (#4107)

Fix missing welcome panel after closing all documents

Closing all documents left the Welcome panel as the only tab, but the old active document index could still point to a tab that no longer existed. The fix is to reset it to 0 when the document list becomes empty.

frontend/src/stores/portfolio.ts

@@ -66,6 +66,7 @@ export function createPortfolioStore(subscriptions: SubscriptionsRouter, editor:
 	subscriptions.subscribeFrontendMessage("UpdateOpenDocumentsList", (data) => {
 		update((state) => {
 			state.documents = data.openDocuments;
+			if (state.documents.length === 0) state.activeDocumentIndex = 0;
 			return state;
 		});
 	});