Add missing thread roles in SearchModel

This fixes the message search so it works again!

(cherry picked from commit 08a0fbfd6b)

src/models/searchmodel.h

@@ -85,6 +85,8 @@ public:
         MimeTypeRole,
         ShowLinkPreviewRole,
         LinkPreviewRole,
+        IsThreadedRole,
+        ThreadRootRole,
     };
     Q_ENUM(Roles)
     explicit SearchModel(QObject *parent = nullptr);