Add a function to check if the handled pointer is NULL.

src/sdl/texture.cpp

@@ -343,6 +343,11 @@ void ttexture::update_pixels(SDL_Surface *surf)
 	}
 }
 
+bool ttexture::null() const
+{
+	return texture_ == NULL;
+}
+
 void ttexture::initialise_from_surface(SDL_Renderer& renderer, const int access)
 {
 	if(access == SDL_TEXTUREACCESS_STATIC) {

src/sdl/texture.hpp

@@ -281,6 +281,13 @@ public:
 	 */
 	 void update_pixels(SDL_Surface* surf);
 
+	 /**
+	  * Tells whether the instance really handles an SDL_Texture object.
+	  *
+	  * @return                   True if the handled pointer is NULL.
+	  */
+	 bool null() const;
+
 private:
 	/**
 	 * The reference count of the texture.