[jdk11u-dev] RFR: 8223143: Restructure/clean-up for 'loopexit_or_null()'.

[Martin Doerr]

Clean backport of JDK-8223143.

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Commit messages:
 - Backport 8088ed83178ef8b0e4be6d510f28bd6bb1beecc8

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/861/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=861&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8223143
  Stats: 42 lines in 1 file changed: 23 ins; 1 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/861.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/861/head:pull/861

PR: https://git.openjdk.java.net/jdk11u-dev/pull/861