ASAR Integrity assumes a single asar file is present

[t3chguy]

An application may use multiple ASARs and want integrity for all of them, but merging packages using @electron/universal breaks that.

Related electron-userland/electron-builder#8660

The main process code lives in app.asar and the renderer/webapp code lives in webapp.asar (for complicated reasons). We'd like integrity enabled at least on the app.asar but it seems like the fuse applies to all ASARs, and due to merging universal packages causing the integrity to get clobbered that is problematic.

[7727:0122/164306.527723:FATAL:archive.cc(239)] Failed to get integrity for validatable asar archive: Resources/webapp.asar

[mmaietta]

Note to the electron devs, I'm happy to pick up working on this issue after #117. 🙃 I just rewrote electron-builders asar integrity calculation to handle multi-asar project setups, so it should be easy to port over to electron/universal.