RFR: 8324232: KeyEvent.getCode() is null inside JFXPanel

[Martin Fox]

JavaFX uses a table to map from an AWT integer key code to a JavaFX KeyCode. If AWT provides a code that's not in the table JavaFX attempts to use a KeyCode of null when constructing the KeyEvent which raises an exception.  This PR just checks for null and changes it to KeyCode.UNDEFINED.

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Commit messages:
 - Merge remote-tracking branch 'upstream/master' into fxpanelkeycode
 - An unrecognized key should produce KeyCode.UNDEFINED, not null.

Changes: https://git.openjdk.org/jfx/pull/1470/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1470&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324232
  Stats: 7 lines in 1 file changed: 5 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1470.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1470/head:pull/1470

PR: https://git.openjdk.org/jfx/pull/1470