RFR: 8136895: Writer not closed with disk full error, file resource leaked

[Brian Burkhalter]

In`StreamEncoder::implClose`, move `flushLeftoverChar()` inside the `try` block and the closing of the underlying stream inside the `finally` block.

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Commit messages:
 - 8136895: Writer not closed with disk full error, file resource leaked

Changes: https://git.openjdk.org/jdk/pull/13503/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13503&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8136895
  Stats: 97 lines in 2 files changed: 93 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13503.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13503/head:pull/13503

PR: https://git.openjdk.org/jdk/pull/13503