Why abort when Received UUID set?

What is the purpose of aborting when the Received UUID is set?

[Line 5365](https://github.com/digint/btrbk/blob/v0.27.1/btrbk#L5364):
```
if($svol->{node}{received_uuid} ne '-') {
ABORTED($svol, "\"Received UUID\" is set");
WARN "Skipping subvolume \"$svol->{PRINT}\": $abrt";
next;
}
```
Is this really necessary?

Start in btrbk around line 5365 and trace how received_uuid is populated and used before the abort. Compare the surrounding subvolume handling to determine why this guard exists and whether the current behavior is still required. Done means the rationale and any needed behavior change are established in the issue or an associated change.

Written by the indexing model from the issue text.