Currently if a request has set Expect-Continue and receives a non 100 response the `responseMessage` wouldn't be set.
This PR sets `responseMessage`, it also updates `getResponseMessage` to check if the message has already been set. This should match the way that `responseCode` is currently handled. I also added a test to cover some possible responses. ------------- Commit messages: - Response Message could be null Changes: https://git.openjdk.org/jdk/pull/25999/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25999&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8352502 Stats: 195 lines in 3 files changed: 195 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/25999.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/25999/head:pull/25999 PR: https://git.openjdk.org/jdk/pull/25999
