Fix crash caused by incorrect group saved

Should fix #491 and others

src/timeline2/model/groupsmodel.cpp

@@ -820,7 +820,7 @@ int GroupsModel::fromJson(const QJsonObject &o, Fun &undo, Fun &redo)
             }
             ids.insert(fromJson(c.toObject(), undo, redo));
         }
-        if (ids.count(-1) > 0) {
+        if (ids.count(-1) > 0 || type == GroupType::Selection) {
             return -1;
         }
         return groupItems(ids, undo, redo, type);
@@ -924,7 +924,6 @@ bool GroupsModel::fromJsonWithOffset(const QString &data, const QMap<int, int> &
         }
         ok = ok && fromJson(elem.toObject(), local_undo, local_redo);
     }
-    
     if (ok) {
         UPDATE_UNDO_REDO(local_redo, local_undo, undo, redo);
     } else {