fix nifty to support non rgba images in non-gles backends

[riccardobl]

No description provided.

[gemini-code-assist]

Code Review

This pull request removes the GLES-specific platform check in JmeBatchRenderBackend.loadImage, causing the RGBA8 conversion logic to run unconditionally on all platforms when the texture format is not Format.RGBA8. The reviewer correctly identified that this can lead to runtime crashes (UnsupportedOperationException) when loading compressed textures (like DXT or ETC) because ImageRaster does not support them, and suggested adding a check using ImageRaster.isSupported to prevent this issue.

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[github-actions]

🖼️ Screenshot tests have failed.

The purpose of these tests is to ensure that changes introduced in this PR don't break visual features. They are visual unit tests.

📄 Where to find the report:

• Direct Download: screenshot-test-report
• Alternatively, go to the failed run summary > Artifacts > screenshot-test-report
• Download the zip and open jme3-screenshot-tests/build/reports/ScreenshotDiffReport.html

⚠️ If you didn't expect to change anything visual:
Fix your changes so the screenshot tests pass.

✅ If you did mean to change things:
Review the replacement images in jme3-screenshot-tests/build/changed-images to make sure they really are improvements and then replace and commit the replacement images at jme3-screenshot-tests/src/test/resources.

✨ If you are creating entirely new tests:
Find the new images in jme3-screenshot-tests/build/changed-images and commit the new images at jme3-screenshot-tests/src/test/resources.

Note; it is very important that the committed reference images are created on the build pipeline, locally created images are not reliable. Similarly tests will fail locally but you can look at the report to check they are "visually similar".

See https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-screenshot-tests/README.md for more information

Contact @richardTingle (aka richtea) for guidance if required