set frameset size when frame indicies are added

src/Sprite.cpp

@@ -940,6 +940,7 @@ Frameset::Frameset(Sprite* sprite) : sprite(sprite) {}
 void Frameset::add_frame_indicies(int index)
 {
     order.push_back(index);
+    set_size();
 }
 
 void Frameset::set_frame_length(float length)

src/extension.cpp

@@ -400,7 +400,7 @@ SDL_Texture* sfw::get_pixel_scaled_texture(SDL_Renderer* renderer, SDL_Texture*
     if ((SDL_SetRenderTarget(renderer, base)) < 0)
     {
         print_sdl_error("could not set render target to remapped texture");
-        return NULL;
+        return nullptr;
     }
     glm::ivec2 size = get_texture_box(base).get_size();
     Uint32 format = SDL_PIXELFORMAT_RGBA32;