Paket crash when --no-install is specified on update with generate_include_scripts

[matthid]

Description

Original report: fsprojects/FAKE#1672
But this reproduces with paket standalone as well...

This issue only reproduces when a clear state is used (ie packages, paket-files and paket.lock as well as .paket/load deleted):

paket.dependencies

source https://api.nuget.org/v3/index.json
generate_load_scripts: true
nuget Fake.Core.Targets prerelease

group External
    source https://api.nuget.org/v3/index.json

    nuget Google.Protobuf.Tools prerelease

.paket/paket.exe update --no-install --group Main

Paket failed with
-> Folder C:\proj\testing\packages\runtime.ubuntu.16.04-x64.runtime.native.System.Security.Cryptography.OpenSsl doesn't exist. Did you restore groups Main?

Expected behavior

Paket executes a restore even when --no-install is specified.

Actual behavior

Paket doesn't execute a restore and obviously fails when trying to generate load scripts.

Known workarounds

do a restore after the error.