UnInverted cache uses term freq to filter out terms (but deleted docs are included in the freq count) [LUCENE-4242]

TermEnum.docFreq() count is used to compute uninverted index
(DocTermOrds.uninvert()). The code goes like:

final int df = te.docFreq();
if (df <= maxTermDocFreq) {

So, if there are deleted documents in the index and maxTermDocFreq is
low, then the term will be excluded (even if the freq of the livedocs
is OK). Most likely, the cache will be incomplete.

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Migrated from [LUCENE-4242](https://issues.apache.org/jira/browse/LUCENE-4242) by Roman Chyla, updated Jul 24 2012
Attachments: [LUCENE-4242.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-4242/LUCENE-4242.patch) (versions: 3)

Start in DocTermOrds.uninvert() at the TermEnum.docFreq() and maxTermDocFreq filtering described in the issue, then review the attached LUCENE-4242.patch. Verify behavior with deleted documents and confirm that terms are not incorrectly excluded when the live-document frequency is within the limit.

Written by the indexing model from the issue text.