RFR: 8283379: Memory leak in FileHeaderHelper

[Zhengyu Gu]

Please review this small patch to fix memory leak in `FileHeaderHelper`

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Commit messages:
 - Merge branch 'master' into JDK-8283379-memleak-FileHeaderHelper
 - 8283379: Memory leak in FileHeaderHelper

Changes: https://git.openjdk.java.net/jdk/pull/7872/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7872&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283379
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7872.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7872/head:pull/7872

PR: https://git.openjdk.java.net/jdk/pull/7872