getPath in DirectoryTaxonomyReader should throw an exception [LUCENE-9460] #10500
Description
This issue is a spillover from LUCENE-9450 PR and was suggested by @mikemccand
If the ordinal is out of bound it indicates that the user called their main IndexReader and the TaxonomyReader in the wrong order.
In this case, we should throw an IllegalArgumentException to warn the user instead of returning null
Migrated from LUCENE-9460 by Gautam Worah (@gautamworah96), updated Aug 31 2021