Disable safari and share toolbar buttons when no articles are selected

Multiplatform/Shared/SceneModel.swift

@@ -123,6 +123,8 @@ private extension SceneModel {
 		guard !articles.isEmpty else {
 			readButtonState = nil
 			starButtonState = nil
+			openInBrowserButtonState = nil
+			shareButtonState = nil
 			return
 		}