Request's Content-Type charset should not be taken into account when checking available parsers

[michal-m]

Often request's Content-Type header includes charset setting, e.g.:

Content-Type: application/x-www-form-urlencoded; charset=UTF-8
                                                 ^^^^^^^^^^^^^

It should not be taken into account when checking against available request body parsers.

This references #9 reported by @Flyder