RFR: 8227257: javax/swing/JFileChooser/4847375/bug4847375.java fails with AssertionError

[Tejesh R]

Observation found when _JFileChooser_ is instantiated in _WindowsLookAndFeel_ which invokes _getSystemIcon()_ from WindowsFileChooserUI class. Could not find the exact root cause so predicting it to be an issue with icons not loaded where _resolutionVariants_ map is empty in _public Image getResolutionVariant(double width, double height) _. Hence proposing a null check before accessing _getWidth()_. Fix is tested in CI system.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/11079/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11079&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8227257
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11079.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11079/head:pull/11079

PR: https://git.openjdk.org/jdk/pull/11079