[lworld] Integrated: 8350630: [lworld] ObjBufferAllocator::initialize fails with assert(has_klass_gap()) failed: precondition

[Frederic Parain]

Small fix to adjust Valhalla memory allocator to new code from mainline.
More details in the CR.

-------------

Commit messages:
 - Fix memory initialization in allocator

Changes: https://git.openjdk.org/valhalla/pull/1379/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1379&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350630
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/1379.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1379/head:pull/1379

PR: https://git.openjdk.org/valhalla/pull/1379