Dead code: XCResultFile.exportPayload never returns nil #388

XCResultKit.XCResultFile.exportPayload(id:) returns its temp path unconditionally — the underlying exportAttachment is @discardableResult and its failure is never checked.

So the guard let savedURL = file.exportPayload(id: id) else { … } fault branches in ResultFile.exportPayload and exportPayloadData are unreachable. Every genuine export failure actually surfaces later, as the moveItem throw.

Task: either remove the dead branches, or (better) detect real export failure properly — checking that the temp file exists and is non-empty before attempting the move. Relates to the --legacy migration issue, since that will change this API surface anyway.