fix config error if $HOME is None

-not seen on travis due to HOME being manually set to /tmp

lbrynet/conf.py

@@ -507,11 +507,10 @@ def get_linux_directories() -> typing.Tuple[str, str, str]:
     try:
         with open(os.path.join(user_config_dir(), 'user-dirs.dirs'), 'r') as xdg:
             down_dir = re.search(r'XDG_DOWNLOAD_DIR=(.+)', xdg.read()).group(1)
-            down_dir = re.sub('\$HOME', os.getenv('HOME'), down_dir)
+        down_dir = re.sub('\$HOME', os.getenv('HOME') or os.path.expanduser("~/"), down_dir)
         download_dir = re.sub('\"', '', down_dir)
     except EnvironmentError:
         download_dir = os.getenv('XDG_DOWNLOAD_DIR')
-
     if not download_dir:
         download_dir = os.path.expanduser('~/Downloads')