RFR: 8364088: ToolBarSkin: NPE in select()

[Andy Goryachev]

Fixed an NPE in the ToolBar, looks like a corner case.

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Commit messages:
 - npe

Changes: https://git.openjdk.org/jfx/pull/1857/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1857&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364088
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1857.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1857/head:pull/1857

PR: https://git.openjdk.org/jfx/pull/1857