Avoid generating bad remote SQL for INSERT ... DEFAULT VALUES.

"INSERT INTO foo() VALUES ()" is invalid syntax, so don't do that.

contrib/postgres_fdw/deparse.c

@@ -505,6 +505,9 @@ deparseInsertSql(StringInfo buf, PlannerInfo *root, Index rtindex,
 
 	appendStringInfoString(buf, "INSERT INTO ");
 	deparseRelation(buf, rte->relid);
+
+	if (targetAttrs)
+	{
 		appendStringInfoString(buf, "(");
 
 		first = true;
@@ -537,6 +540,9 @@ deparseInsertSql(StringInfo buf, PlannerInfo *root, Index rtindex,
 		}
 
 		appendStringInfoString(buf, ")");
+	}
+	else
+		appendStringInfoString(buf, " DEFAULT VALUES");
 
 	if (returningList)
 		deparseReturningList(buf, root, rtindex, rel, returningList);