Content-Type should be optional for all 3xx redirects

[f-w]

When response is a redirect (302 by default), for example await options.httpContext.res.redirect(redirectUrl) generates following error

(node:8972) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:541:11)
    at ServerResponse.header (C:\Users\x\myProject\node_modules\express\lib\response.js:771:10)
    at HttpContext.done (C:\Users\x\myProject\node_modules\strong-remoting\lib\http-context.js:574:9)
    ...

This PR makes Content-Type header optional since message body is optional for redirects.

Checklist

👉 Read and sign the CLA (Contributor License Agreement) 👈

• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• Commit messages are following our guidelines

[slnode]

Can one of the admins verify this patch? To accept patch and trigger a build add comment ".ok\W+to\W+test."

[bajtos]

Thank you @f-w for the pull request. Let's start by adding a test to reproduce the problem, verify the fix, and prevent regressions in the future.

[bajtos]

We will also need you to sign our Contributor License Agreement before we can accept your patch, see https://cla.strongloop.com/agreements/strongloop/strong-remoting

[f-w]

@bajtos, I have added test case, verified it failed before and works after.
Also signed license agreement.

[dhmlau]

@slnode test please

[dhmlau]

@f-w, for CLA, the author (meaning GitHub id) of all the commits needs to sign the CLA. It seems like you used two account to do the commits?

Please also fix the commit linter error:

**************************************************
**
**  Linting commit logs
**
**  1 problems found:
**    a8a58cd - Content-Type should be optional for all 3xx redirec: First line should be 50 characters or less (saw 53)
**
**************************************************

Reference:

• our commit message guideline: https://loopback.io/doc/en/contrib/git-commit-messages.html
• instructions on amend commit message: https://help.github.com/en/github/committing-changes-to-your-project/changing-a-commit-message

[f-w]

@dhmlau I have addressed both CLA and commit msg length issue.

[dhmlau]

@slnode test please

[bajtos]

Thank you @f-w for adding a test, the changes LGTM now 👏

[bajtos]

Published in [email protected] 🎉