bpo-43323: Fix UnicodeEncodeError in the email module (GH-32137)

It was raised if the charset itself contains characters not encodable
in UTF-8 (in particular \udcxx characters representing non-decodable
bytes in the source).

Lib/email/_header_value_parser.py

@@ -781,7 +781,7 @@ class MimeParameters(TokenList):
                     else:
                         try:
                             value = value.decode(charset, 'surrogateescape')
-                        except LookupError:
+                        except (LookupError, UnicodeEncodeError):
                             # XXX: there should really be a custom defect for
                             # unknown character set to make it easy to find,
                             # because otherwise unknown charset is a silent