RFR: 8336879: Always true condition 'img != null' in GTKPainter.paintPopupMenuBackground [v2]

[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:

  Review comment fix

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/20308/files
  - new: https://git.openjdk.org/jdk/pull/20308/files/e4cb9c22..d97e9c76

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20308&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20308&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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