Ensure we don't raise events for options changing to unsubscribed callers

We were grabbing the list of subscriptions before scheduling the event
back to the UI thread. This meant we might raise events on the UI thread
for somebody who has already unsubscribed on the UI thread.

Fixes #13862.

src/Workspaces/Core/Portable/Options/OptionServiceFactory.cs

@@ -65,17 +65,16 @@ public void OnWorkspaceDisposed(Workspace workspace)
 
             private void OnGlobalOptionServiceOptionChanged(object sender, OptionChangedEventArgs e)
             {
-                var eventHandlers = GetEventHandlers();
-                if (eventHandlers.Length > 0)
+                _taskQueue?.ScheduleTask(() =>
                 {
-                    _taskQueue?.ScheduleTask(() =>
+                    // Ensure we grab the event handlers inside the scheduled task to prevent a race of people unsubscribing
+                    // but getting the event later on the UI thread
+                    var eventHandlers = GetEventHandlers();
+                    foreach (var handler in eventHandlers)
                     {
-                        foreach (var handler in eventHandlers)
-                        {
-                            handler(this, e);
-                        }
-                    }, "OptionsService.SetOptions");
-                }
+                        handler(this, e);
+                    }
+                }, "OptionsService.SetOptions");
             }
 
             private ImmutableArray<EventHandler<OptionChangedEventArgs>> GetEventHandlers()
@@ -98,7 +97,7 @@ private ImmutableArray<EventHandler<OptionChangedEventArgs>> GetEventHandlers()
 
                 remove
                 {
-                    lock(_gate)
+                    lock (_gate)
                     {
                         _eventHandlers = _eventHandlers.Remove(value);
                     }