[utils] Fix intlist_to_bytes in Python 2 (#4181)

youtube_dl/utils.py

@@ -843,10 +843,7 @@ def bytes_to_intlist(bs):
 def intlist_to_bytes(xs):
     if not xs:
         return b''
-    if isinstance(chr(0), bytes):  # Python 2
-        return ''.join([chr(x) for x in xs])
-    else:
-        return bytes(xs)
+    return struct.pack('%dB' % len(xs), *xs)
 
 
 # Cross-platform file locking