Libwalletqt: integrate changes from upstream

Co-authored-by: xiphon <xiphon@protonmail.com>

src/utils/scheduler.cpp

@@ -68,6 +68,11 @@ QPair<bool, QFuture<void>> FutureScheduler::run(std::function<void()> function)
 //    });
 //}
 
+bool FutureScheduler::stopping() const noexcept
+{
+    return Stopping;
+}
+
 bool FutureScheduler::add() noexcept
 {
     QMutexLocker locker(&Mutex);