fix(usermodel): create a copy of the original notification errors list

`ActivityListModel::removeActivityFromActivityList` mutates the
reference to the list returned by `ActivityListModel::errorsList` which
may result in undefined behaviour during each iteration...

Signed-off-by: Jyrki Gadinger <[email protected]>

Author: nilsding

src/gui/tray/usermodel.cpp

@@ -588,7 +588,7 @@ void User::slotProgressInfo(const QString &folder, const ProgressInfo &progress)
             return;
         const auto &engine = f->syncEngine();
         const auto style = engine.lastLocalDiscoveryStyle();
-        for (const auto &activity : _activityModel->errorsList()) {
+        for (const auto errorsList = _activityModel->errorsList(); const auto &activity : errorsList) {
             if (activity._expireAtMsecs != -1) {
                 // we process expired activities in a different slot
                 continue;