Reproduction steps:
1. Open the attached project.
2. Select 'neg_rg.tiff'.
3. Try different Format options in the Inspector and click Apply after each selection.

Actual behavior (Screenshots attached):
- Notice, that only 'RGB HDR Compressed BC6H' shows a green square with a smaller black square in the corner.
- Customer_example.exr has various -ve values, normal -ve are fine, but -0.0 and very small values are the bad blocks.

Expected behavior:
- SImilar behavior between different compression Formats using Linear Color Space.

Workaround:
- Add a -ve 0 check in ClampHDRSafe

Reproduced with:
2017.2.3p1, 2017.4.6f1, 2018.1.6f1, 2018.2.0b9, 2018.3.0a2