RFR: 8371386: Fix potential NPE in SwingNode

[Prasanta Sadhukhan]

There can be potential NPEs in SwingNode which is fixed

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Commit messages:
 - 8371386: Fix potential NPE in SwingNode

Changes: https://git.openjdk.org/jfx/pull/1965/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1965&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371386
  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1965.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1965/head:pull/1965

PR: https://git.openjdk.org/jfx/pull/1965