Switching focus to graph while updating event dispatcher tooltip in details view causes text to be reverted.

`TreeView->ClearSelection()` gets called before the text is set/committed. `FBlueprintDelegateActionDetails::GetDelegateProperty` which calls `SMyBlueprint::SelectionAsDelegate` requires the TreeView to have a selection set, otherwise it fails.

1. Create a new Actor BP
2. Within the Actor BP, create a new event delegate and select it
3. Inside the details panel of the delegate, type in a text within the `tooltip` field
4. While the text edit field still has focus, left-click on the graph view
5. Text reverts back to what it had before