RFR: 8264162: PickResult.toString() is missing the closing square bracket

[Kevin Rushforth]

Simple fix to add a missing closing bracket to `PickResult::toString`. This includes a unit test that fails without the fix and passes with the fix.

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Commit messages:
 - 8264162: PickResult.toString() is missing the closing square bracket

Changes: https://git.openjdk.java.net/jfx/pull/443/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=443&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264162
  Stats: 33 lines in 2 files changed: 33 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/443.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/443/head:pull/443

PR: https://git.openjdk.java.net/jfx/pull/443