Remote server: URI /results without "Accept" header results in 404

**Citrus Version**
2.7.6

**Expected behavior**
The service should default to serving "application/json" or give code 400 Bad Request, maybe with some explaining.

**Actual behavior**
The service returns 404, which might lead the caller to think he got the wrong path.

**Test case sample**
> Please, share the test case (as small as possible) which shows the issue
Just do a curl .../integration-citrus-test/results once with "Accept: application/json" and once without.

Start by reproducing the issue with curl against integration-citrus-test/results, once with Accept: application/json and once without. Trace the remote server endpoint handling and make the missing header produce application/json or a 400 Bad Request response with an explanation; done means the endpoint no longer returns 404 for this case.

Written by the indexing model from the issue text.