fix: infinite loop if go.mod not found, warn on missing go.mod or forgotten go get

[a-h]

Fixes #418

[joerdav]

I'm wondering if the lack of a go.mod should not be an error. Since they are an optional feature of go.

[a-h]

Although it prints an error if the go.mod is not present, it doesn't actually stop anything @joerdav

[joerdav]

Ah yeah, it doesn't exist just a warning log, I forgot about that one! Cool LGTM

[joerdav]

One thing, the test project could go in a testdata folder, then it'll only ever be compiled on test runs.