Steps to repro:
1. Open the attached project RealtimeGIBug and SampleScene scene;
2. In the Preferences window (Edit>Preferences>GI Cache) click Clean Cache button;
3. In the Lighting window (Window>Rendering>Lighting) click Generate Lighting button;
4. Wait until scene's realtime GI finishes baking;
5. In the Lighting window open Realtime Lightmaps tab and double-click on any lightmap thumbnail to open the Lightmap Preview window;
6. In the opened Lightmap preview window expand the dropdown list at the top right corner of the window and select UV Charts option.

Expected result:
UV Charts texture visualization is opened without errors in the Console.

Actual result:
UV Charts texture visualization is not opened and is stuck on loading. The following errors are shown in the Console:
- "Unknown file extension; template function should be specialized."
- "Failed reading from: '95/95cb3b26217c14cc23c2af213c38cfd6.unknown'."
- "'Runtime Texture' job failed with error code: 5 ('Failed creating texture data.')."
Regression introduced in Version 2021.2.0.

Notes:
- Reproducible in 2022.1.0a3, 2021.2.0b5;
- Not reproducible in 2019.4.29f1, 2020.1.17f1, 2020.2.7f1-dots, 2020.3.15f1, 2021.1.16f1;
- Reproducible on Windows;
- Reproducible only in the Lightmap preview window; UV charts are shown as expected when opening the corresponding Scene view Editor visualization filter;
- Reproducible only for Realtime GI lightmaps, not reproducible for Baked GI lightmaps.