RFR: 8251481: TableCell accessing row: NPE on auto-sizing

[Marius Hanl]

This PR will fix a simple NPE which may happens when using the `TableRow` inside a `TableCell` during the initial auto sizing.
In the auto sizing code, no `TableRow` is set, therefore `getTableRow()` will return null and it is not possible to e.g. access the row item.

This is fixed by adding the `TableRow` in the `resizeColumnToFitContent` method, similar as it is already done for the `TreeTableView` (`TreeTableRow`).

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Commit messages:
 - 8251481: TableCell accessing row: NPE on auto-sizing

Changes: https://git.openjdk.java.net/jfx/pull/716/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=716&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251481
  Stats: 28 lines in 2 files changed: 26 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/716.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/716/head:pull/716

PR: https://git.openjdk.java.net/jfx/pull/716