Graphics/SpriteLibrary: Fix missing initialization/uninitialization (fixes crash at exit)

Former-commit-id: c7bbd781d163a8456f1fadd0f71451adc5a1bd1a

include/Nazara/Graphics/Sprite.hpp

@@ -23,6 +23,9 @@ namespace Nz
 
 	class NAZARA_GRAPHICS_API Sprite : public InstancedRenderable
 	{
+		friend SpriteLibrary;
+		friend class Graphics;
+
 		public:
 			inline Sprite();
 			inline Sprite(MaterialRef material);
@@ -57,6 +60,9 @@ namespace Nz
 			void MakeBoundingVolume() const override;
 			void UpdateData(InstanceData* instanceData) const override;
 
+			static bool Initialize();
+			static void Uninitialize();
+
 			Color m_color;
 			MaterialRef m_material;
 			Rectf m_textureCoords;