Fixed disable tasks for .NET 3

IPA.Loader/Loader/PluginManager.cs

@@ -15,6 +15,7 @@ using Logger = IPA.Logging.Logger;
 using System.Threading.Tasks;
 #if NET4
 using TaskEx = System.Threading.Tasks.Task;
+using TaskEx6 = System.Threading.Tasks.Task;
 using Task = System.Threading.Tasks.Task;
 #endif
 #if NET3
@@ -177,7 +178,7 @@ namespace IPA.Loader
                         else 
                         {
                             if (exec.Executor.Metadata.RuntimeOptions != RuntimeOptions.DynamicInit)
-                                return TaskEx.FromException(new CannotRuntimeDisableException(exec.Executor.Metadata));
+                                return TaskEx6.FromException(new CannotRuntimeDisableException(exec.Executor.Metadata));
 
                             var res = TaskEx.WhenAll(exec.Dependents.Select(d => Disable(d, alreadyDisabled)))
                                  .ContinueWith(t => TaskEx.WhenAll(t, exec.Executor.Disable())).Unwrap();

Net3-Proxy/Net3-Proxy.csproj

@@ -48,6 +48,7 @@
     <Compile Include="IReadOnlyList.cs" />
     <Compile Include="Path.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="TaskEx6.cs" />
     <Compile Include="Tuple.cs" />
     <Compile Include="TypeUtils.cs" />
     <Compile Include="Utils.cs" />

Net3-Proxy/TaskEx6.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Net3_Proxy
+{
+    public static class TaskEx6
+    {
+        public static Task<TResult> FromException<TResult>(Exception exception)
+        {
+            if (exception == null) throw new ArgumentNullException(nameof(exception));
+            var tcs = new TaskCompletionSource<TResult>();
+            tcs.TrySetException(exception);
+            return tcs.Task;
+        }
+        public static Task FromException(Exception exception) => FromException<VoidTaskResult>(exception);
+
+        private struct VoidTaskResult { }
+    }
+}