[foreign-memaccess+abi] RFR: Fix TestSegmentAllocators

[Maurizio Cimadamore]

This patch fixes a test which started to fail as we have changed the delegation order in the SegmentAllocator methods.

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Commit messages:
 - Fix TestSegmentAllocators

Changes: https://git.openjdk.org/panama-foreign/pull/867/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=867&range=00
  Stats: 23 lines in 1 file changed: 0 ins; 17 del; 6 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/867.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/867/head:pull/867

PR: https://git.openjdk.org/panama-foreign/pull/867