We saw a case where the recovery stats reported `recovered_bytes` greater than `length_in_bytes` for one file:

```
GET /_recovery?detailed

200 OK
...
{
  "name": "_buk.fdt",
  "length_in_bytes": 26891307173,
  "reused": false,
  "recovered_in_bytes": 35324928266,
  "recovered_from_snapshot_in_bytes": 8433621093
}
...
```

NB `35324928266 == 26891307173 + 8433621093`

This causes Elasticsearch to compute a negative value for the reserved space on the target node of this recovery, which prevents stats APIs from working. This appears to be caused by a network-level failure which triggers a retry without first cancelling an ongoing download of a different file with the same name from the snapshot repository.

---

### Workaround

Restart the target node to clear these stats.
server/src/main/java/org/elasticsearch/index/shard/IndexShard.java
assert Thread.holdsLock(mutex);
        assert newPrimaryTerm > pendingPrimaryTerm || (newPrimaryTerm >= pendingPrimaryTerm && combineWithAction != null);
        assert getOperationPrimaryTerm() <= pendingPrimaryTerm;
        final CountDownLatch termUpdated = new CountDownLatch(1);
        asyncBlockOperations(new ActionListener<Releasable>() {
            @Override
            public void onFailure(final Exception e) {
                try {
                    innerFail(e);
                } finally {
                    if (combineWithAction != null) {
                        combineWithAction.onFailure(e);
                    }
                }
            }
            private void innerFail(final Exception e) {
                try {
                    failShard("exception during primary term transition", e);
                } catch (AlreadyClosedException ace) {
                    
                }
            }
            @Override
            public void onResponse(final Releasable releasable) {
                final Releasable releaseOnce = Releasables.releaseOnce(releasable);
                try {
                    assert getOperationPrimaryTerm() <= pendingPrimaryTerm;
                    termUpdated.await();