RFR: JDK-8298147: Clang warns about pointless comparisons

[Thomas Stuefe]

Trivial fix for clang warnings. GET_CONTAINER_INFO_CPTR creates local buffers of the given size; comparing them with NULL will always yield the same result.

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Commit messages:
 - JDK-8298147-clang-warns-about-pointless-compares

Changes: https://git.openjdk.org/jdk/pull/11544/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11544&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298147
  Stats: 27 lines in 2 files changed: 0 ins; 27 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11544.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11544/head:pull/11544

PR: https://git.openjdk.org/jdk/pull/11544