ClassCastException in BytesStore.ramBytesUsed [LUCENE-7629]

```Java
Caused by: java.lang.ClassCastException: [I cannot be cast to [B
at org.apache.lucene.util.fst.BytesStore.ramBytesUsed(BytesStore.java:478)
at org.apache.lucene.util.fst.FST.ramBytesUsed(FST.java:436)
at org.apache.lucene.codecs.blocktree.FieldReader.ramBytesUsed(FieldReader.java:187)
at org.apache.lucene.codecs.blocktree.BlockTreeTermsReader.ramBytesUsed(BlockTreeTermsReader.java:309)
at org.apache.lucene.codecs.perfield.PerFieldPostingsFormat$FieldsReader.ramBytesUsed(PerFieldPostingsFormat.java:238)
at org.apache.lucene.index.SegmentCoreReaders.ramBytesUsed(SegmentCoreReaders.java:226)
at org.apache.lucene.index.SegmentReader.ramBytesUsed(SegmentReader.java:614)
at org.apache.solr.handler.admin.LukeRequestHandler.getIndexHeapUsed(LukeRequestHandler.java:579)
at org.apache.solr.handler.admin.LukeRequestHandler.getIndexInfo(LukeRequestHandler.java:558)
at org.apache.solr.handler.admin.CoreAdminHandler.getCoreStatus(CoreAdminHandler.java:1135)
at org.apache.solr.handler.admin.CoreAdminHandler.handleStatusAction(CoreAdminHandler.java:699)
... 29 more
```

Saw this running Solr on a patched 4.10.3.

I have not been able to reproduce this, but it seems similar to what was reported at https://discuss.elastic.co/t/strange-marvel-exception/36112

---
Migrated from [LUCENE-7629](https://issues.apache.org/jira/browse/LUCENE-7629) by Mike Drob (@madrob)
Environment:
```
Oracle jdk1.8.0_74 (64-bit) with G1GC
```