Fix setting project on existing issue

While working on netbeans redmine integration, I noticed, that I failed to change the project for an issue. I could track it down to using the project identifier, instead of the id of the project when creating the request object.

I created a unittest, that demonstrates the problem and verifies the fix.

The fix is intended to support the "old" way and the new way - the idea: As long a project ID is present, use that, if it is not present, fall back to the identifier. All unittests still pass.