[3.5] bpo-37461: Fix infinite loop in parsing of specially crafted email headers...

[3.5] bpo-37461: Fix infinite loop in parsing of specially crafted email headers (GH-14794) (#15446)

* [3.5] bpo-37461: Fix infinite loop in parsing of specially crafted email headers (GH-14794)

Some crafted email header would cause the get_parameter method to run in an
infinite loop causing a DoS attack surface when parsing those headers. This
patch fixes that by making sure the DQUOTE character is handled to prevent
going into an infinite loop.
(cherry picked from commit a4a994bd3e619cbaff97610a1cee8ffa87c672f5)

Co-authored-by: Abhilash Raj <maxking@users.noreply.github.com>
Co-Authored-By: Ashwin Ramaswami <aramaswamis@gmail.com>