fix potential IndexOutOfBoundsException in *Classifier.getClasses(?,int) [LUCENE-8110]

KNearestNeighborDocumentClassifier already has the [one-line fix](https://github.com/apache/lucene-solr/blob/releases/lucene-solr/7.2.0/lucene/classification/src/java/org/apache/lucene/classification/document/KNearestNeighborDocumentClassifier.java#L102) via [SOLR-8871](https://issues.apache.org/jira/browse/SOLR-8871) and this ticket here is to add the same to the remaining Classifier classes.

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Migrated from [LUCENE-8110](https://issues.apache.org/jira/browse/LUCENE-8110) by Christine Poerschke (@cpoerschke)
Attachments: [LUCENE-8110.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-8110/LUCENE-8110.patch)

Start with KNearestNeighborDocumentClassifier.java at the linked getClasses entry point, then inspect the remaining Classifier implementations mentioned in the issue. Compare the existing SOLR-8871 fix and the attached LUCENE-8110.patch. Done means the remaining classes no longer have the reported IndexOutOfBoundsException risk and their relevant tests pass.

Written by the indexing model from the issue text.