Add an early out to `ktxTexture2_TranscodeBasis` when `outputFormat` is ASTC_HDR_4x4 and the texture format is UASTC_HDR_4X4

[MarkCallow]

Add a check to ktxTexture2_TranscodeBasis so that it returns immediately if outputFormat is KTX_TTF_ASTC_HDR_4x4_RGBA and the texture's colorModel is KHR_DF_MODEL_UASTC_HDR_4X4.

Originally posted by @MarkCallow in #1100 (comment)

[ViNeek]

How early should this exit?

The documentation for ktxTexture2_TranscodeBasis mentions that:

The transcoded images replace the original images and the texture's fields including the DFD are modified to reflect the new format

So if someone requests transcoding to KTX_TTF_ASTC_HDR_4x4_RGBA, should the texture be updated to reflect the new format (in headers, formats e.t.c.) or should we simply return immediately without touching either the data or the metadata.

Or should we only take an early exit right before the decoding part?

[MarkCallow]

So if someone requests transcoding to KTX_TTF_ASTC_HDR_4x4_RGBA, should the texture be updated to reflect the new format (in headers, formats e.t.c.) or should we simply return immediately without touching either the data or the metadata.

The before and after format is identical with the exception of the colorModel, channel id (and, IIRC, the sign qualifier on the channel) so I was thinking return immediately but it is more semantically correct to update the colorMode, channel id and sign qualifier. The reason I want an early return is because of cubemaps, arrays and 3d textures. For example I have a cubemap with 72 images.