This PR fixes a nullpointer in TableSkinUtils that occured when the Tables items were null.
------------- Commit messages: - JDK-8323543: adds similar safety test in TreeTableViewTest - JDK-8323543: Fixes Nullpointer in TableSkinUtils Changes: https://git.openjdk.org/jfx/pull/1329/files Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1329&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8323543 Stats: 53 lines in 4 files changed: 41 ins; 11 del; 1 mod Patch: https://git.openjdk.org/jfx/pull/1329.diff Fetch: git fetch https://git.openjdk.org/jfx.git pull/1329/head:pull/1329 PR: https://git.openjdk.org/jfx/pull/1329
