fixed: the application crashes when the user used the x button or key combination to close the window

the crash occured because running state was set false but the
application loop was still running during that frame and rendered to the
now closed window, because the check only happened at the start of the
next frame

SakuraCore/src/Application.cpp

@@ -135,6 +135,9 @@ void Application::Run() {
             }
         }
 
+        if (!m_isRunning) {
+            break;
+        }
         // Rendering
 
         for (auto &layer : m_LayerStack) {