1-Authentication/6-sign-in-node-cli-app : Configure.ps1 script error - attempts to assign owner when owner is null

original code:

```
if ($owner -eq $null)
{
New-MgApplicationOwnerByRef -ApplicationId $currentAppObjectId -BodyParameter @{"@odata.id" = "https://graph.microsoft.com/v1.0/directoryObjects/$user.ObjectId"}
Write-Host "'$($user.UserPrincipalName)' added as an application owner to app '$($clientServicePrincipal.DisplayName)'"
}
```

should be
```
if ($owner -ne $null)
```