Model: Allow creating an interface with empty name

But don't allow such a tunnel to be added to the tunnel manager.

(We'll need to create an interface with an empty name when we're reading QR codes.)

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

WireGuard/WireGuard/UI/TunnelViewModel.swift

@@ -98,7 +98,7 @@ class TunnelViewModel {
 
         func save() -> SaveResult<InterfaceConfiguration> {
             fieldsWithError.removeAll()
-            guard let name = scratchpad[.name] else {
+            guard let name = scratchpad[.name], (!name.isEmpty) else {
                 fieldsWithError.insert(.name)
                 return .error("Interface name is required")
             }