RFR: 8221334: TableViewSkin: must initialize flow's cellCount in constructor

[Jeanette Winzenburg]

This is a fix for https://bugs.openjdk.java.net/browse/JDK-8221334

- fixed as outlined in the bug report: added updateItemCount() in skin constructor (that's what all sibling skins are doing)
- added test which fails for TableViewSkin before, passes after the fix

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Commits:
 - 55e588c7: 8221334: TableViewSkin: must initialize flow's cellCount in constructor

Changes: https://git.openjdk.java.net/jfx/pull/56/files
 Webrev: https://webrevs.openjdk.java.net/jfx/56/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8221334
  Stats: 113 lines in 2 files changed: 113 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/56.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/56/head:pull/56

PR: https://git.openjdk.java.net/jfx/pull/56