fix(apple): don't return Data() to fetchResources (#10605)

When the tunnel first comes up, the first call to `fetchResources` was
returning an empty `Data()` instance that the receiver would fail to
decode properly because it assumes if a `Data` is non-nil, it is a list
of Resources.

This resulted in a decode error each time the tunnel was started.

Related:
https://github.com/firezone/firezone/pull/10603#discussion_r2438472011

---------

Signed-off-by: Jamil <jamilbk@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

swift/apple/FirezoneNetworkExtension/Adapter.swift

@@ -297,24 +297,22 @@ class Adapter: @unchecked Sendable {
       guard let self = self else { return }
 
       // Convert uniffi resources to FirezoneKit resources and encode with PropertyList
-      let propertyListData: Data
-      if let uniffiResources = self.resources {
-        let firezoneResources = uniffiResources.map { self.convertResource($0) }
-        guard let encoded = try? PropertyListEncoder().encode(firezoneResources) else {
-          Log.log("Failed to encode resources as PropertyList")
-          completionHandler(nil)
-          return
-        }
-        propertyListData = encoded
-      } else {
-        propertyListData = Data()
+      guard let uniffiResources = self.resources
+      else { return completionHandler(nil) }
+
+      let firezoneResources = uniffiResources.map { self.convertResource($0) }
+
+      guard let encoded = try? PropertyListEncoder().encode(firezoneResources)
+      else {
+        Log.log("Failed to encode resources as PropertyList")
+        return completionHandler(nil)
       }
 
-      if hash == Data(SHA256.hash(data: propertyListData)) {
+      if hash == Data(SHA256.hash(data: encoded)) {
         // nothing changed
         completionHandler(nil)
       } else {
-        completionHandler(propertyListData)
+        completionHandler(encoded)
       }
     }
   }