macOS: Tunnels list: Don't allow empty selection

Signed-off-by: Roopesh Chander <roop@roopc.net>

WireGuard/WireGuard/UI/macOS/ViewController/TunnelsListTableViewController.swift

@@ -19,6 +19,7 @@ class TunnelsListTableViewController: NSViewController {
         tableView.headerView = nil
         tableView.rowSizeStyle = .medium
         tableView.allowsMultipleSelection = true
+        tableView.allowsEmptySelection = false
         return tableView
     }()