RFR: 8203463: [Accessibility, Narrator] NPE in TableView

[eduardsdv]

The NullPointer occurs when `Accessible.getAttribute(Object)` returns null. 
I checked all places where the `getAttribute(..)` method is called. Everywhere it is checked for null `(Accessible,` `MacAccessible,` `WinAccessible,` `WinTextRangeProvider`). Only at this one place in `WinAccessible.GetPatternProvider(int)` it is missing.

This PR adds this missing null-check in the `WinAccessible.GetPatternProvider(int)` method.

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Commit messages:
 - Merge branch 'openjdk:master' into bugfix/8203463-NPE-in-WinAccessible-GetPatternProvider
 - WinAccessible: Add missing null check

Changes: https://git.openjdk.java.net/jfx/pull/700/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=700&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8203463
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/700.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/700/head:pull/700

PR: https://git.openjdk.java.net/jfx/pull/700