If the WebFlux handler commits the response but still sends an error
signal in the reactive pipeline, Spring Boot error handling should not
try to handle that error: once committed, it is impossible to change the
response status or the response headers. Writing to the body might also
lead to invalid responses.

This commit skips error handling if the response is committed and
delegates to Spring Framework's `HttpWebHandlerAdapter` which will log
the error.

Fixes gh-11168