[socks] Fix error reporting (#11355)

youtube_dl/socks.py

@@ -60,7 +60,7 @@ class ProxyError(IOError):
 
     def __init__(self, code=None, msg=None):
         if code is not None and msg is None:
-            msg = self.CODES.get(code) and 'unknown error'
+            msg = self.CODES.get(code) or 'unknown error'
         super(ProxyError, self).__init__(code, msg)