fixed: 不传退回目标节点直接退回至开始节点

src/Hotline.Application/Orders/OrderApplication.cs

@@ -5183,7 +5183,9 @@ public class OrderApplication : IOrderApplication, IScopeDependency
             userId = prevStep.HandlerId;
             orgId = prevStep.HandlerOrgId;
             roles = [prevStep.RoleId];
-        } while (sendBack.AssignStepId != prevStep.Id && prevStep.StepType is not EStepType.Start);
+        } while (!string.IsNullOrEmpty(sendBack.AssignStepId) &&
+                 sendBack.AssignStepId != prevStep.Id &&
+                 prevStep.StepType is not EStepType.Start);
 
         sendBack.ApplyOrgId = currentStep.AcceptorOrgId;
         sendBack.ApplyOrgName = currentStep!.AcceptorOrgName;