Issue with 24-bit TGA texture banding fix

[BC46]

Commit https://github.com/FLHDE/freelancer-hd-edition/commit/41fb0198de8406444bb3fbb3f95b291fbe6994a3 is a great addition to the mod since it allows for 24-bit TGA textures to no longer look low-quality. This way it would be possible to convert non-transparent 32-bit TGA textures back to 24-bit TGA to save some space. However, as of this commit, I noticed that the Red Giants now have a black box around them.

It seems this only occurs for the texture lenscircle in sun.txm. I can't explain why it doesn't happen for the other non-transparent sun textures.