Failures if triagebot loses access to an unresolved tracked issue

[bgilbert]

If triagebot loses permission to read an unresolved tracked issue, report generation fails with a traceback. There's not a straightforward way to find the offending issue (other than a manual audit) since the issue key isn't given in the traceback. Further, the affected issue cannot be resolved through the UI; manual database editing is required.

In this case, allow report generation to proceed by omitting the unavailable issue metadata, and allow unconditional resolution of the issue via the UI. If an issue is incorrectly resolved while in this state, and the bot later regains access to the issue, it'll automatically unresolve the issue anyway.