lock when there isnt a package dir either

[cdmistman]

Why

There's still some scenarios when upm lock doesn't happen. Right now the heuristic is:

1. --force flag is passed
2. lockfile doesn't exist
3. specfile has changed

We should also run if the package dir doesn't exist

What Changed

if the 3 above conditions are all false, then also check to see if backend.GetPackageDir() returns a path, and if that path doesn't exist.

Testing

test suite :)

for manual testing:

1. create a npm package
2. add a dependency and lock (however you choose to do this, doesn't matter)
3. rm -rdf node_modules if it exists
4. upm lock should recreate the node_modules dir

[blast-hardcheese]

makes sense