[AltServer] Fixes fetching anisette data on macOS 10.14 Mojave

AltXPC does not work on Mojave, so only attempt it on macOS 10.15 Catalina or later.

AltServer/AnisetteDataManager.swift

@@ -53,22 +53,31 @@ class AnisetteDataManager: NSObject
     
     func requestAnisetteData(_ completion: @escaping (Result<ALTAnisetteData, Error>) -> Void)
     {
-        self.requestAnisetteDataFromXPCService { (result) in
+        if #available(macOS 10.15, *)
-            do
+        {
-            {
+            self.requestAnisetteDataFromXPCService { (result) in
-                let anisetteData = try result.get()
+                do
-                completion(.success(anisetteData))
+                {
-            }
+                    let anisetteData = try result.get()
-            catch CocoaError.xpcConnectionInterrupted
+                    completion(.success(anisetteData))
-            {
+                }
-                // SIP and/or AMFI are not disabled, so fall back to Mail plug-in.
+                catch CocoaError.xpcConnectionInterrupted
-                self.requestAnisetteDataFromPlugin { (result) in
+                {
-                    completion(result)
+                    // SIP and/or AMFI are not disabled, so fall back to Mail plug-in.
+                    self.requestAnisetteDataFromPlugin { (result) in
+                        completion(result)
+                    }
+                }
+                catch
+                {
+                    completion(.failure(error))
                 }
             }
-            catch
+        }
-            {
+        else
-                completion(.failure(error))
+        {
+            self.requestAnisetteDataFromPlugin { (result) in
+                completion(result)
             }
         }
     }
@@ -87,6 +96,7 @@ class AnisetteDataManager: NSObject
 
 private extension AnisetteDataManager
 {
+    @available(macOS 10.15, *)
     func requestAnisetteDataFromXPCService(completion: @escaping (Result<ALTAnisetteData, Error>) -> Void)
     {
         guard let proxy = self.xpcConnection.remoteObjectProxyWithErrorHandler({ (error) in