RFR: 8284680: sun.font.FontConfigManager.getFontConfig() leaks charset

[Zhengyu Gu]

Please review this small patch that releases temporary charsets to avoid memory leak.

Test:

- [x] jdk_2d

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Commit messages:
 - v0

Changes: https://git.openjdk.java.net/jdk/pull/8187/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8187&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284680
  Stats: 10 lines in 1 file changed: 9 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8187.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8187/head:pull/8187

PR: https://git.openjdk.java.net/jdk/pull/8187