Fix some minor blunders.

Fixes #4853 (faulty initialization) and fixes #4681 (unsupported GLSL version).

src/core/Application.cpp

@@ -96,6 +96,7 @@ void Application::Run()
 {
 	Profiler::Clock m_runtime{};
 	m_runtime.Start();
+	m_applicationRunning = true;
 
 	Startup();
 

src/pigui/PiGui.cpp

@@ -218,7 +218,11 @@ void PiGui::Init(SDL_Window *window)
 		Error("RENDERER_DUMMY is not a valid renderer, aborting.");
 		return;
 	case Graphics::RENDERER_OPENGL_3x:
+#ifdef __APPLE__
+		ImGui_ImplOpenGL3_Init("#version 140");
+#else
 		ImGui_ImplOpenGL3_Init();
+#endif
 		break;
 	}