Issue extras: be clear when an issue version doesn't exist

[MarceloRobert]

In the issue extras endpoint, the first_incident is independent of the version, but the trees and tags aren't.
If the issue_id passed exists, but the combination issue_id + issue_version doesn't, then the first_incident will return, but the rest of the data won't.

The response should be refactored such that the version data isn't returned if the issue_id + issue_version doesn't exist. The first_incident data should still be returned, along with the version of that first_incident.

[MarceloRobert]

Also try to explore other options for those cases. Such as returning an error, not returning the data for that issue, or something else.