Reproduction steps:

1. Create a new project
2. Force Quit Unity
3. Open the "ShaderCompiler.log" inside of the Projects Library folder

Expected Result: The Shader Compiler process should end without any unhandled exceptions if Force Closed
Actual Result: "Unhandled exception: Protocol error - failed to read correct magic number" is thrown

Fixed in: 2018.1.0a3

Reproduced with: 2017.3.0b1, 2017.2.0f1, 2017.1.1p2, 5.6.3p3, 5.5.4p5