Fix Jetty and Undertow customizers to restore Spring Boot 2.0 behavior where a negative or zero `max-http-header-size` indicates that the server default should be used. Closes gh-14986
Fix Jetty and Undertow customizers to restore Spring Boot 2.0 behavior where a negative or zero `max-http-header-size` indicates that the server default should be used. Closes gh-14986