Throw if the manager isn't ready so that windows use their cached data instead

Author: shana

src/GitHub.Api/Git/Repository.cs

@@ -82,7 +82,7 @@ public ITask SetupRemote(string remote, string remoteUrl)
         public ITask<List<GitLogEntry>> Log()
         {
             if (repositoryManager == null)
-                return new FuncListTask<GitLogEntry>(TaskHelpers.GetCompletedTask(new List<GitLogEntry>()));
+                return new FuncListTask<GitLogEntry>(new NotReadyException().ToTask<List<GitLogEntry>>());
 
             return repositoryManager.Log();
         }

src/GitHub.Api/Helpers/TaskHelpers.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Threading.Tasks;
 
 namespace GitHub.Unity
@@ -8,5 +9,16 @@ public static Task<T> GetCompletedTask<T>(T result)
         {
             return TaskEx.FromResult(result);
         }
+
+        public static Task<T> ToTask<T>(this Exception exception)
+        {
+          TaskCompletionSource<T> completionSource = new TaskCompletionSource<T>();
+          completionSource.TrySetException(exception);
+          return completionSource.Task;
+        }
+    }
+
+    public class NotReadyException : Exception
+    {
     }
 }