RFR: 7903583: JOL: Heap dump parser misses superclasses with empty fields

[Aleksey Shipilev]

[CODETOOLS-7903579](https://bugs.openjdk.org/browse/CODETOOLS-7903579) was not complete for old layouter. There are still problems when superclasses do not have fields.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jol/pull/54/files
 Webrev: https://webrevs.openjdk.org/?repo=jol&pr=54&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903583
  Stats: 17 lines in 3 files changed: 14 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jol/pull/54.diff
  Fetch: git fetch https://git.openjdk.org/jol.git pull/54/head:pull/54

PR: https://git.openjdk.org/jol/pull/54