RFR: 8282628: Potential memory leak in sun.font.FontConfigManager.getFontConfig()

[Zhengyu Gu]

Please review this small patch that fixes a potential memory leak that exception return fails to release allocated `cacheDirs`

Test:

- [x] jdk_desktop on Linux x86_64

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Commit messages:
 - 8282628: Potential memory leak in sun.font.FontConfigManager.getFontConfig()

Changes: https://git.openjdk.java.net/jdk/pull/7691/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7691&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282628
  Stats: 21 lines in 2 files changed: 18 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7691.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7691/head:pull/7691

PR: https://git.openjdk.java.net/jdk/pull/7691