Reproduction steps:
1. Create a new project
2. In the Project settings navigate to Quality settings tab
3. Delete all the Quality Levels
4. Set the Texture Quality to Eight Res

Expected result: Hierarchy and Project window icons do not become pixelated when Quality Levels are deleted and Texture Quality is set to Eight Res
Actual result: Hierarchy and Project window icons become pixelated when Quality Levels are deleted and Texture Quality is set to Eight Res

Reproducible with: 2018.4.35f1, 2019.4.27f1, 2020.2.7f1, 2020.3.9f1, 2021.2.0a2, 2021.2.0a17
Not reproducible with: 2021.1.0a1, 2021.1.8f1, 2021.2.0a1

Notes:
-One Quality Level will remain and cannot be deleted
-Texture Quality dropdown setting has a typo, "Eighth Res" should be "Eight Res"
-In 2018.4 the Project window folder icons do not get pixelated while GameObject icons still do