fix black_hostname_list work error issue when config black_hostname_list is empty

shadowsocks/asyncdns.py

@@ -276,7 +276,7 @@ class DNSResolver(object):
         self._hostname_to_cb = {}
         self._cb_to_hostname = {}
         self._cache = lru_cache.LRUCache(timeout=300)
-        # TODO read black_hostname_list from config
+        # read black_hostname_list from config
         if type(black_hostname_list) != list:
             self._black_hostname_list = []
         else:

shadowsocks/shell.py

@@ -262,6 +262,8 @@ def get_config(is_local):
     else:
         config['server'] = to_str(config.get('server', '0.0.0.0'))
         config['black_hostname_list'] = to_str(config.get('black_hostname_list', '')).split(',')
+        if len(config['black_hostname_list']) == 1 and config['black_hostname_list'][0] == '':
+            config['black_hostname_list'] = []
         try:
             config['forbidden_ip'] = \
                 IPNetwork(config.get('forbidden_ip', '127.0.0.0/8,::1/128'))