bpo-33524: Fix the folding of email header when max_line_length is 0 or None (#13391)

and there are non-ascii characters in the header.

Lib/email/_header_value_parser.py

@@ -68,6 +68,7 @@ XXX: provide complete list of token types.
 """
 
 import re
+import sys
 import urllib   # For urllib.parse.unquote
 from string import hexdigits
 from operator import itemgetter
@@ -2590,7 +2591,7 @@ def _refold_parse_tree(parse_tree, *, policy):
 
     """
     # max_line_length 0/None means no limit, ie: infinitely long.
-    maxlen = policy.max_line_length or float("+inf")
+    maxlen = policy.max_line_length or sys.maxsize
     encoding = 'utf-8' if policy.utf8 else 'us-ascii'
     lines = ['']
     last_ew = None

Lib/email/policy.py

@@ -3,6 +3,7 @@ code that adds all the email6 features.
 """
 
 import re
+import sys
 from email._policybase import Policy, Compat32, compat32, _extend_docstrings
 from email.utils import _has_surrogates
 from email.headerregistry import HeaderRegistry as HeaderRegistry
@@ -203,7 +204,7 @@ class EmailPolicy(Policy):
     def _fold(self, name, value, refold_binary=False):
         if hasattr(value, 'name'):
             return value.fold(policy=self)
-        maxlen = self.max_line_length if self.max_line_length else float('inf')
+        maxlen = self.max_line_length if self.max_line_length else sys.maxsize
         lines = value.splitlines()
         refold = (self.refold_source == 'all' or
                   self.refold_source == 'long' and