[jfx11u] Integrated: 8263807: Button types of a DialogPane are set twice, returns a wrong button

[Kevin Rushforth]

Clean backport.

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Commit messages:
 - 8263807: Button types of a DialogPane are set twice, returns a wrong button

Changes: https://git.openjdk.java.net/jfx11u/pull/58/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=58&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263807
  Stats: 52 lines in 2 files changed: 45 ins; 3 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/58.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/58/head:pull/58

PR: https://git.openjdk.java.net/jfx11u/pull/58