RFR: 8352268: [TestBug] Saving in Rich Editor Demo

[Andy Goryachev]

Fixes embarrassing bugs in Rich Editor Demo:

- File -> Save not saving
- File -> Open not emphasizing .rich files

-------------

Commit messages:
 - save

Changes: https://git.openjdk.org/jfx/pull/1739/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1739&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352268
  Stats: 17 lines in 1 file changed: 6 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jfx/pull/1739.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1739/head:pull/1739

PR: https://git.openjdk.org/jfx/pull/1739