RFR: 8289171: Blank final field 'dialog' may not have been initialized in scene.control.Dialog:521

[Andy Goryachev]

- changed initialization sequence

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Commit messages:
 - 8289171: proper initialization sequence

Changes: https://git.openjdk.org/jfx/pull/815/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=815&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289171
  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/815.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/815/head:pull/815

PR: https://git.openjdk.org/jfx/pull/815