Clean backport for 8160597: IllegalArgumentException when we initiate drag on Image
------------- Commit messages: - 8160597: IllegalArgumentException when we initiate drag on Image Changes: https://git.openjdk.java.net/jfx11u/pull/63/files Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=63&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8160597 Stats: 157 lines in 5 files changed: 156 ins; 0 del; 1 mod Patch: https://git.openjdk.java.net/jfx11u/pull/63.diff Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/63/head:pull/63 PR: https://git.openjdk.java.net/jfx11u/pull/63
