AssertFail in badger file on db close

[AndrewSisley]

Has started happening in the change detector recently, happens in TestQueryOneToOneWithGroupRelatedIDFromSecondary most (but not all) of the time. Removing the last query removes the assert fail.

Might be a badger bug, as they seem to have had issues in the past: dgraph-io/badger#1350

If the request in the test is modified:

This fails:

Request: `query {
	Book {
		name
	}
}`,

This works:

Request: `query {
	Author {
		name
	}
}`,

• Removing either one of the Author create actions removes/hides the problem.
• Removing lines 874-891 (where secondary id creation is handled) from collection.go has no impact.
• Removing the Lens fetcher has no impact.
• Updating to badger v4.1.0 has no impact
• Exiting before calling fetcher.FetchNextDoc in scan node removes the error, suggesting that fetcher.Init and fetcher.Start are not relevant in this issue.
• Exiting immediately after the FetchNext call in FetchNextDoc has no impact, suggesting FetchNext is responsible
• Removing the filter stuff from FetchNext has no impact, suggesting it's irrelevance
• Returning an error anywhere within the last 4 lines of fetcher.nextKey removes the assert failure
• Calling nextKV 8 times results in the failure, calling it 7 times does not. The key on the 8th value is /1/v/bae-d6627fea-8bf7-511c-bcf9-bac4212bddd6/v
• Calling df.kvResultsIter.NextSync() in nextKVRaw a 9th time results in the problem, regardless of whether the value is ignored or not