title: How to determine if an WPF Datagrid item is selected, and bind to the true/false result
body: <p>I feel like this should be easy, but I am stumped.</p>
  
  <p>I am trying to bind a ComboBox.IsEnabled property to something like "Is an item currently selected on the DataGrid" property using MVVM. This way if no item is selected on the DataGrid, the ComboBox will be disabled.</p>
  
  <p>Is there a DataGrid property that registers True/False when an item is selected, or do I need to do something with the SelectedItems.Count property? </p>
  
  <p>I am trying to do this with as little code as possible before I write a converter or custom property.</p>