Reproduction steps:
1. Open the attached project (Crunched Textures Error.zip);
2. Open the Demo.unity scene;
3. Make sure that the picture is Read/Write Enabled;
4. Press the play button to enter play mode;
5. Then press again to quit play mode;
6. Observe errors in the console.

Expected results: the function GetPixels() works with any type of texture or image;
Actual results: GetPixels() is not able to read the crunched format of the texture;

Reproduced on: 5.3.5.p8, 5.4.3f1, 5.5.0f2, 5.6.0a5.

By Design: crunched textures can't be partially decompressed, so it is not possible make GetPixel[s] work efficiently.