`--noNimblePath` should unconditionally be set for projects with lock files

[arnetheduck]

If a project has a lock file, plain nim and tooling should be prevented from ever looking into the nimble folder, so as to avoid that random code from the global nimble cache infects the project.

The current strategy with a conditional when fileExists("nimble.paths"): breaks before nimble setup has been run, because nimble.paths does not exist on a freshly cloned repository.