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.
diff --git a/Lib/email/policy.py b/Lib/email/policy.py
index 5131311ac..611deb5 100644
--- a/Lib/email/policy.py
+++ b/Lib/email/policy.py
@@ -3,6 +3,7 @@
 """
 
 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 @@
     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