Fix usersettings hook if data === undefined

When I run the seed data, I get several error messages when I want to
delete my account. The error that is fixed with this commit is
```
Cannot read property 'blacklist' of undefined
```

Another error which pops up is
```
Cannot read property 'Forbidden' of undefined
```
This error is **NOT** resolved with this commit. Fortunately, some
resources get deleted when the user pushes the button, so all you have
to do is to click the "delete account" button multiple times.

Author: roschaefer

server/services/usersettings/hooks/validate-blacklist.js

@@ -3,6 +3,7 @@ const { BadRequest } = require('@feathersjs/errors');
 const validateBlacklist = () => {
   return async (hook) => {
     const { data } = hook;
+    if (!data) return hook;
     const blacklist = data.blacklist;
     if (!blacklist) return hook;
     const userId = data.userId;