Related/similar to UNDERTOW-1540

The user in this forum thread https://developer.jboss.org/message/989396#989396 notes that the reader/writer obtained via the request/response on a servlet doesn't use the correct charset, when the charset is set at the ServletContext level (through the use of setRequestCharacterEncoding and/or setResponseCharacterEncoding)

Looking at the code in HttpServletRequestImpl and HttpServletResponseImpl there indeed seems to be a bug.