fix undefined error caused by npm outdated -g

[firedfox]

Following error is shown when npm outdated -g is called:

npm ERR! Cannot read property 'length' of undefined

This patch fixes the problem by setting path to an empty string when tree.package.name is undefined.

[Teamop]

Already fixed in #173

[Zearin]

It’s been fixed in #173 for ages. Since 2019-03-20, in fact.

So, why is it taking so long to publish this bugfix?

[firedfox]

Here’s an update on what’s been happening with the open PRs https://gist.github.com/aeschright/8ed09cbc2a4aee00fcb4ad35086d76a6
I'll close this PR and just wait

[ljharb]

No point in closing the PR; waiting would be appropriate.