Bad Accept-Language request headers can result in NPE during HttpServletRequest.getLocale() call

**Jetty version(s)**
12.0.27

**Jetty Environment**
core, ee8, ee9, ee10+

**Java version/vendor** `(use: java -version)`
Any

**OS type/version**
Any

**Description**
If a bad `Accept-Language` request header is received, it can result in an NPE when fetching the locale of the request.

* from Servlet API `HttpServletRequest.getLocale()`
* from Core API `Request.getLocales(Request)`





