Modify write file interface (#712)

* add core dump

* add core dump

* fix cpplint

* vit check

* merge master

Author: lipanpan03

include/lgraph/olap_on_db.h

@@ -1525,18 +1525,21 @@ class OlapOnDB : public OlapBase<EdgeData> {
             if (output_filter != nullptr && !output_filter(i, vertex_data[i])) {
                 continue;
             }
-            auto vit = txn_.GetVertexIterator(OriginalVid(i));
-            auto vit_label = vit.GetLabel();
-            auto primary_field = txn_.GetVertexPrimaryField(vit_label);
-            auto field_data = vit.GetField(primary_field);
-            json curJson;
-            curJson["vid"] = OriginalVid(i);
-            curJson["label"] = vit_label;
-            curJson["primary_field"] = primary_field;
-            curJson["field_data"] = field_data.ToString();
-            curJson["result"] = vertex_data[i];
-            auto content = curJson.dump() + "\n";
-            fout.Write(content.c_str(), content.size());
+            auto vit = txn_.GetVertexIterator();
+            vit.Goto(OriginalVid(i));
+            if (vit.IsValid()) {
+                auto vit_label = vit.GetLabel();
+                auto primary_field = txn_.GetVertexPrimaryField(vit_label);
+                auto field_data = vit.GetField(primary_field);
+                json curJson;
+                curJson["vid"] = OriginalVid(i);
+                curJson["label"] = vit_label;
+                curJson["primary_field"] = primary_field;
+                curJson["field_data"] = field_data.ToString();
+                curJson["result"] = vertex_data[i];
+                auto content = curJson.dump() + "\n";
+                fout.Write(content.c_str(), content.size());
+            }
         }
     }