fixed error to copy again to cache dir

Author: tikuma-lsuhsc

src/ffmpeg_downloader/_backend.py

@@ -194,7 +194,7 @@ def do(filename, url, content_type, size, *cache_info):
                     copyfile(zippath, cache_info[0])
 
                 # move the downloaded file to the final destination
-                if not zippath.startswith(dst):
+                if no_cache_dir or not cache_info[0].startswith(dst):
                     move(zippath, dst)
             elif cache_info[0] != dstpath:
                 # if not downloading to the cache dir, copy the file