Fix thread no-stop bug

src/device/DeviceManager.cpp

@@ -300,3 +300,8 @@ void DeviceManager::processScan(const char* json, bool empty) {
 	THROW_ERROR(errmsg);
 	qDebug() << ">>>>>>>>>>>>>>>>>>>>>ScanControl failed";
 }
+
+void DeviceManager::close() {
+    previewDataCaller->terminate();
+    delete previewDataCaller;
+}