Codesigning error, it is trying to sign a binary file that is splitted in parts

[augustnmonteiro]

Squirrel version(s)
2.0.1

Description
I'm using a lib that divides it's binary file into 3 files, the first one gets signed fine, the 2,3 files it seems like that it doesn't get signed because of the mime type, could we check if the mime type is valid before sending it to the signtool?

Steps to recreate

1. start electron project with electron-forge
2. add nut.js https://github.com/nut-tree/nut.js
3. make the project with a certificate configuration

Expected behavior
Sign only files that can be signed

Actual behavior
It is trying to sign the whole folder

Additional information
for reference the lib we are using it is https://github.com/nut-tree/libnut

[anaisbetts]

Squirrel doesn't care about or use MIME types, it would be helpful if you could describe how this library works in more detail