Fix race condition within HandleWorkflowError

Also adds a more sensible caption to the error dialog when non-workflow errors occur.

Bonsai.Editor/EditorForm.cs

@@ -1407,6 +1407,7 @@ bool HandleSchedulerError(Exception e)
 
         void HandleWorkflowError(Exception e)
         {
+            var building = this.building; // Ensure the current value of `building` is used when if the handler below is invoked
             Action selectExceptionNode = () =>
             {
                 var workflowException = e as WorkflowException;
@@ -1415,7 +1416,7 @@ void HandleWorkflowError(Exception e)
                     workflowError = workflowException;
                     HighlightExceptionBuilderNode(workflowException, building);
                 }
-                else editorSite.ShowError(e.Message, Name);
+                else editorSite.ShowError(e.Message, "Internal workflow error");
             };
 
             if (InvokeRequired) BeginInvoke(selectExceptionNode);