fix: do not throw on missing package.json

[ruyadorno]

This fixes running npm exec in folders that does not have a package.json since runScript throws a ENOENT error.

NOTE: Not sure if throwing a ENOENT error on missing package.json is the intended behavior, if that's the case we can also simply patch its usage in npm exec by providing the empty pkg: {scripts:{}} arg 🤔

[nlf]

it makes sense to me to patch this here, though we should maybe only catch and try again if the error is ENOENT? as is, if you have a package.json but it's invalid we would lose that signal

[ruyadorno]

tbh the more I think about it the more I think it makes more sense to patch it in lib/exec.js instead. The empty {scripts: {}} dance is already there, the problem is just that the usage added to support already installed pkgs gets triggered before that dance is set up.

I'll try to float a PR in the cli instead (the more annoying part is the unit tests there I guess) and close this one if that turns out to work well.

[ruyadorno]

closing in favor of: npm/cli#2081