RFR: 8159055: ImageIcon.setImage can't handle null parameter

[Prasanta Sadhukhan]

When trying to call 'icon.setImage(null);' where 'icon' is an instance of ImageIcon, a null pointer exception is thrown at runtime.
The code tried to get the `id` for that image and instantiates `MediaTracker` to associate the null image to that `id` and checks the status of loading this null image, removes the null image from the tracker and then tries to get the image width where it throws NPE as image is null.

It's better to not go through all MediaTracker usage and bail out initially itself for null image..

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Commit messages:
 - COpyright
 - ImageIcon.setImage can't handle null parameter

Changes: https://git.openjdk.org/jdk/pull/25767/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25767&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8159055
  Stats: 47 lines in 2 files changed: 46 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25767.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25767/head:pull/25767

PR: https://git.openjdk.org/jdk/pull/25767