RESTEASY-2831: Check mediatype before calling isCompatible

[Pastor]

I have got NPE when call logout method in keycloak 20.0.3. It occurs when calling BaseHttpRequest.getFormParameters and Content-Type is not set.

[jamezp]

Thank you @Pastor. We require all contributions to be made under the terms of the ASL 2.0 License: http://www.apache.org/licenses/LICENSE-2.0
Do you agree to these terms?

[Pastor]

Thank you @Pastor. We require all contributions to be made under the terms of the ASL 2.0 License: http://www.apache.org/licenses/LICENSE-2.0 Do you agree to these terms?

Yes, of course