RFR: 8266426: ZHeapIteratorOopClosure does not handle native access properly

[Albert Mingkun Yang]

Early return for native pointers in `ZHeapIteratorOopClosure::load_oop`.

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Commit messages:
 - iterator

Changes: https://git.openjdk.java.net/jdk/pull/3838/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3838&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266426
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3838.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3838/head:pull/3838

PR: https://git.openjdk.java.net/jdk/pull/3838