[jfx11u] Integrated: 8274929: Crash while reading specific clipboard content

[Kevin Rushforth]

Clean backport to `jfx11u`.

-------------

Commit messages:
 - 8274929: Crash while reading specific clipboard content

Changes: https://git.openjdk.java.net/jfx11u/pull/60/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=60&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274929
  Stats: 115 lines in 3 files changed: 111 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/60.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/60/head:pull/60

PR: https://git.openjdk.java.net/jfx11u/pull/60