[lworld] RFR: 8253663: [lworld] [lw3] TestJNIArrays crashes in jni_CreateSubElementSelector

[Frederic Parain]

Please review this small changeset fixing two naked oops in the JNI code to access flattened arrays.
These fixes should prevent the crashes we recently saw with TestJNIArrays test.

Tested with Mach5, tiers 1 to 3.

Thank you,

Fred

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Commit messages:
 - Fix naked oop

Changes: https://git.openjdk.java.net/valhalla/pull/200/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=200&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253663
  Stats: 6 lines in 1 file changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/200.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/200/head:pull/200

PR: https://git.openjdk.java.net/valhalla/pull/200