RFR: 8349516: StAXStream2SAX.handleCharacters() fails on empty CDATA

[Joe Wang]

Fix handleCharacters by adding a guard to zero length and letting the rest of the process continue (e.g. closing tags and etc).

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Commit messages:
 - 8349516: StAXStream2SAX.handleCharacters() fails on empty CDATA

Changes: https://git.openjdk.org/jdk/pull/23847/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23847&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349516
  Stats: 54 lines in 2 files changed: 51 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/23847.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23847/head:pull/23847

PR: https://git.openjdk.org/jdk/pull/23847