[1.5.x] Fixed #20169 -- Ensured that the WSGI request's path is correctly...

[1.5.x] Fixed #20169 -- Ensured that the WSGI request's path is correctly based on the `SCRIPT_NAME` environment parameter or the `FORCE_SCRIPT_NAME` setting, regardless of whether or not those have a trailing slash. Thanks to bmispelon for the review.
Backport of 2f81a0ca