[lworld] RFR: 8261647: [lworld] Missing default initialization of non-flattened field of empty inline type

[Tobias Hartmann]

After [JDK-8253893](https://bugs.openjdk.java.net/browse/JDK-8253893) has been fixed, I've re-enabled some compiler tests for empty inline types and noticed that they are failing. The problem is that both during slow path array access through `OptoRuntime::load_unknown_inline()` and when re-allocating during deoptimization, non-flattened fields of an empty inline type are not properly initialized with the default value.

Best regards,
Tobias

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Commit messages:
 - 8261647: [lworld] Missing default initialization of non-flattened field of empty inline type

Changes: https://git.openjdk.java.net/valhalla/pull/335/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=335&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261647
  Stats: 65 lines in 4 files changed: 24 ins; 28 del; 13 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/335.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/335/head:pull/335

PR: https://git.openjdk.java.net/valhalla/pull/335