优化:避免错误

src/Add-on/DrawViewport.ts

@@ -71,7 +71,12 @@ async function GetViewportInfo(): Promise<{ p1: Vector3; p2: Vector3; ens: Entit
             if (rectRes.StringResult === "T")
             {
                 if (ens.length === 0)
+                {
                     ens = await SelectEns();
+
+                    if (!ens)//避免错误
+                        break;
+                }
                 else
                     ens = [];
             }