Renderer: Add a base Initialize() method to match Shutdown()

Source/Core/VideoBackends/OGL/main.cpp

@@ -179,7 +179,8 @@ bool VideoBackend::Initialize(const WindowSystemInfo& wsi)
   g_texture_cache = std::make_unique<TextureCache>();
   g_sampler_cache = std::make_unique<SamplerCache>();
   g_shader_cache = std::make_unique<VideoCommon::ShaderCache>();
-  static_cast<Renderer*>(g_renderer.get())->Init();
+  if (!g_renderer->Initialize())
+    return false;
   TextureConverter::Init();
   BoundingBox::Init(g_renderer->GetTargetWidth(), g_renderer->GetTargetHeight());
   return g_shader_cache->Initialize();