[BUG] No/broken R16G16B16A16 support

[musicalmushr00m]

The issue

R16G16B16A16 "ColorCorrectionTextureHDR" textures are not supported in preview or export.

Reproduction steps

Steps to reproduce the behaviour:

1. Find a R8G8B8A8 texture, for example a LUT, with hash 0018941C98370007
2. Open it and check preview, export as, etc etc. It will preview/export correctly.

In GK preview:

Exported as TGA in Photoshop:

4. Find a R16G16B16A16 texture, for example a LUT, with hash 000B1BC3C75B15D9
5. Open it and check preview, export as, etc etc. It will NOT preview/export correctly.

In GK preview:

Exported as TGA in Photoshop:

Expected behaviour

R16G16B16A16 texture appears correctly when previewed or exported.

Observed behaviour

R16G16B16A16 texture appears as solid grey in editor, and only certain highlights show up in image editors.

Additional context

I believe these textures are supported properly within TonyTools directly.

[atampy25]

The preview is correct behaviour, the texture is entirely transparent so there is nothing to display.

The colour channels exported however do seem to be incorrect - this is a tex-rs issue (@dafitius).