Fix the heap-use-after-free and memory leak

To fix the heap-use-after-free issue when 'screen' is accessed by the
'twin_sdl_work()' function, remove the '_twin_sdl_destroy(screen, tx)'
operation. Additionally, to address the memory leak, add the
'twin_path_destroy(path)' function to ensure the unused path is properly
destroyed. Add the operation to deallocate 'frame', as it will no longer
be used in the future.

Close #49

Author: weihsinyeh

apps/multi.c

@@ -216,6 +216,7 @@ static void apps_jelly_start(twin_screen_t *screen, int x, int y, int w, int h)
             twin_path_destroy(stroke);
         }
     }
+    twin_path_destroy(path);
     twin_window_show(window);
 }
 

backend/sdl.c

@@ -62,8 +62,6 @@ static void _twin_sdl_destroy(twin_screen_t *screen, twin_sdl_t *tx)
     SDL_DestroyRenderer(tx->render);
     SDL_DestroyWindow(tx->win);
     SDL_Quit();
-
-    twin_screen_destroy(screen);
 }
 
 static void twin_sdl_damage(twin_screen_t *screen, twin_sdl_t *tx)

src/image-gif.c

@@ -600,10 +600,12 @@ static twin_animation_t *_twin_animation_from_gif_file(const char *path)
     }
     anim->iter = twin_animation_iter_init(anim);
     if (!anim->iter) {
+        free(frame);
         free(anim);
         gif_close(gif);
         return NULL;
     }
+    free(frame);
     gif_close(gif);
     return anim;
 }