fix: tolerate null bugs URLs

Currently, if the bugs URL returned from `package.json`, which is
processed through
[hosted-git-info](https://github.com/npm/hosted-git-info), is falsy, an
error is thrown. However, hosted-git-info may well return a falsy bugs
URL. This can happen when there is no bugs URL in the repo, but
hosted-git-info tries to infer one, but one cannot be inferred, for
example if the repository URL is a SourceHut URL. This is described
here: npm/hosted-git-info#213

For this reason, we should tolerate falsy URLs and fall back to whatever
is defined in `bugs.js`, in this case being sent to
https://www.npmjs.com/package/<packageName>.

lib/commands/bugs.js

@@ -22,7 +22,10 @@ class Bugs extends PackageUrlCmd {
     // try to get it from the repo, if possible
     const info = this.hostedFromMani(mani)
     if (info) {
-      return info.bugs()
+      const infoUrl = info.bugs();
+      if (infoUrl) {
+        return infoUrl;
+      }
     }
 
     // just send them to the website, hopefully that has some info!