RFR: 8187145: (Tree)TableView with null selectionModel: throws NPE on sorting [v2]

[Andy Goryachev]

> Setting a null selection model in TableView and TreeTableView produce NPE on sorting (and probably in some other situations) because the check for null is missing in several places. 
> 
> Setting a null selection model is a valid way to disable selection in a (tree)table.
> 
> There is also a similar issue with ListView [JDK-8279640](https://bugs.openjdk.org/browse/JDK-8279640).
> 
> changes:
> - added check for null selection model where it was missing
> - clearing focused row index on setting null selection model in TreeTableView

Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:

 - 8187145: clear selection when setting selection model
 - Merge remote-tracking branch 'origin/master' into 8187145.null.selection.model
 - Merge remote-tracking branch 'origin/master' into 8187145.null.selection.model
 - 8187145: whitespace
 - 8187145: clear focus
 - 8187145: tree table view
 - 8187145: fall through
 - 8187145: check for null selection model

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/876/files
  - new: https://git.openjdk.org/jfx/pull/876/files/df5a2402..d6d185fc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=876&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=876&range=00-01

  Stats: 144 lines in 9 files changed: 123 ins; 3 del; 18 mod
  Patch: https://git.openjdk.org/jfx/pull/876.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/876/head:pull/876

PR: https://git.openjdk.org/jfx/pull/876