[lworld] Integrated: 8254985: [lworld] C2 compilation fails with assert(field_type->is_loaded()) failed: field type must be loaded

[Tobias Hartmann]

Removed the assert which is too strong and added a regression test.

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Commit messages:
 - 8254985: [lworld] C2 compilation fails with assert(field_type->is_loaded()) failed: field type must be loaded

Changes: https://git.openjdk.java.net/valhalla/pull/230/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=230&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254985
  Stats: 26 lines in 2 files changed: 25 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/230.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/230/head:pull/230

PR: https://git.openjdk.java.net/valhalla/pull/230