优化当没有需要下料的吸嘴时程序报错

Rs.SkyLine/Commom/NozzleCollection.cs

@@ -193,7 +193,13 @@ namespace Rs.MotionPlat.Commom
         {
             if (nozzles != null && nozzles.Count > 0)
             {
-                return nozzles.Where(n => n.Status == ENozzleStatus.ToUnload).OrderBy(o=>o.ToType).First();
+                var nozzlelist = nozzles.Where(n => n.Status == ENozzleStatus.ToUnload);
+                if (nozzlelist != null && nozzlelist.Count() > 0)
+                {
+                    return nozzles.Where(n => n.Status == ENozzleStatus.ToUnload).OrderBy(o => o.ToType).First();
+                }
+                else
+                    return null;
             }
             return null;
         }