RFR: 8186904: TableColumnHeader: resize cursor lost on right click

[Marius Hanl]

This PR is fixing a bug, when a right click on a table column is performed. 
By doing that, the table columns will lose the resize cursor thus they can not be resized anymore.

The reason for that is that the **columnDragLock** will not reset (to false).
This flag is set to true, when a mouse press is detected (on a table column) and to false, when a mouse release is detected. Unfortunately, this flag is not reset on a right click, because a check (**#isPopupTrigger()**) will guard against it.

With this PR, this flag will always reset to false inside the mouse released handler.

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

Commit messages:
 - 8186904: Fixed resize cursor got lost when right click table column

Changes: https://git.openjdk.java.net/jfx/pull/483/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=483&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8186904
  Stats: 56 lines in 3 files changed: 50 ins; 3 del; 3 mod
  Patch: https://git.openjdk.java.net/jfx/pull/483.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/483/head:pull/483

PR: https://git.openjdk.java.net/jfx/pull/483