remove need for window argument since we init with one

include/NazaraImgui/NazaraImgui.hpp

@@ -35,7 +35,7 @@ namespace Nz
         ~Imgui();
 
         bool Init(Nz::Window& window, bool bLoadDefaultFont = true);
-        void Update(Nz::Window& window, float dt);
+        void Update(float dt);
         void Render(Nz::RenderTarget* renderTarget, Nz::RenderFrame& frame);
 
         inline ImguiDrawer& GetImguiDrawer() { return m_imguiDrawer; }
@@ -71,6 +71,7 @@ namespace Nz
 
         ImGuiContext* m_currentContext;
         std::string m_clipboardText;
+        Nz::Window* m_window;
 
         bool m_bWindowHasFocus;
         bool m_bMouseMoved;