wait thread to avoid strange OSX behavior failing to lock the mutex

src/node_stroke_preview.cpp

@@ -504,6 +504,7 @@ void NodeStrokePreview::draw_stroke()
         s_running = true;
         s_renderer = std::thread([] {
             BT_SetTerminate();
+            std::this_thread::sleep_for(std::chrono::milliseconds(100));
             App::I.async_start();
             m_sampler_linear.create();
             m_sampler_linear_repeat.create(GL_LINEAR, GL_REPEAT);