Crash if Delivery Group Description is blank

The utility will crash on launch if one or more of your Delivery Groups does not have a description (the Description is empty).

To find affected groups:
```powershell
Get-BrokerDesktopGroup | Where-Object Description -eq $null
```

As a workaround, I removed line 214 from `MainForm.cs` so it doesn't collect the `Description` property:

```csharp
dGroup.Description = desktopGroup.Properties["Description"].Value.ToString();
```

If we still want to collect the Description, please add a null check.