!1346 代码瑕疵存在隐患

Merge pull request !1346 from wangym11/I4GJWP

src/common/backend/parser/parse_utilcmd.cpp

@@ -689,7 +689,7 @@ Oid *namespaceid, bool isFirstNode)
 #else
     if (!IsA(stmt, CreateForeignTableStmt) && !stmt->distributeby && !stmt->inhRelations && cxt.fallback_dist_col) {
 #endif
-        stmt->distributeby = (DistributeBy*)palloc0(sizeof(DistributeBy));
+        stmt->distributeby = makeNode(DistributeBy);
         stmt->distributeby->disttype = DISTTYPE_HASH;
         stmt->distributeby->colname = cxt.fallback_dist_col;
     }