[Rev 02] RFR: 8244112: Skin implementations: must not violate contract of dispose

[Jeanette Winzenburg]

> some skins have not been guarding themselves against multiple calls to dispose (see issue for details)
> 
> Fixed by backing out off dispose if skinnable is null. Added test (parameterized in control class) for all controls in
> the controls package. Those that failed for the misbehaving skins before are passing after the fix.

Jeanette Winzenburg has updated the pull request incrementally with one additional commit since the last revision:

  cleanup as per review

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/209/files
  - new: https://git.openjdk.java.net/jfx/pull/209/files/fe76204d..2a362614

Webrevs:
 - full: https://webrevs.openjdk.java.net/jfx/209/webrev.02
 - incr: https://webrevs.openjdk.java.net/jfx/209/webrev.01-02

  Stats: 4 lines in 2 files changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/209.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/209/head:pull/209

PR: https://git.openjdk.java.net/jfx/pull/209