RFR: 8336879: Always true condition 'img != null' in GTKPainter.paintPopupMenuBackground [v3]

[Abhishek Kumar]

> In GTKPainter.paintPopupMenuBackground method, `img != null` condition will always be true, because it's only checked after `img.getRGB` method is called and that means img can't be `null`.  So, the null check condition is removed. CI testing is ok.

Abhishek Kumar has updated the pull request incrementally with one additional commit since the last revision:

  minor spacing and comment fix

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20308/files
  - new: https://git.openjdk.org/jdk/pull/20308/files/d97e9c76..5c904d9d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20308&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20308&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20308.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20308/head:pull/20308

PR: https://git.openjdk.org/jdk/pull/20308