Fixed bug with EXPLAIN on empty table

mysql-test/r/explain.result

 drop table if exists t1;
 create table t1 (id int not null, str char(10), unique(str));
+explain select * from t1;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	system	NULL	NULL	NULL	NULL	0	const row not found
 insert into t1 values (1, null),(2, null),(3, "foo"),(4, "bar");
 select * from t1 where str is null;
 id	str

mysql-test/t/explain.test

@@ -3,6 +3,7 @@
 
 drop table if exists t1;
 create table t1 (id int not null, str char(10), unique(str));
+explain select * from t1;
 insert into t1 values (1, null),(2, null),(3, "foo"),(4, "bar");
 select * from t1 where str is null;
 select * from t1 where str="foo";
@@ -12,8 +13,10 @@ explain select * from t1 ignore key (str) where str="foo";
 explain select * from t1 use key (str,str) where str="foo";
 
 #The following should give errors
-!$1072 explain select * from t1 use key (str,str,foo) where str="foo";
-!$1072 explain select * from t1 ignore key (str,str,foo) where str="foo";
+--error 1072
+explain select * from t1 use key (str,str,foo) where str="foo";
+--error 1072
+explain select * from t1 ignore key (str,str,foo) where str="foo";
 drop table t1;
 
 explain select 1;

sql/sql_select.cc

@@ -7352,7 +7352,9 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       
       if (tab->info)
 	item_list.push_back(new Item_string(tab->info,strlen(tab->info)));
-      else if (tab->select)
+      else
+      {
+	if (tab->select)
 	{
 	  if (tab->use_quick == 2)
 	  {
@@ -7382,6 +7384,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 	if (buff_ptr == buff)
 	  buff_ptr+= 2;
 	item_list.push_back(new Item_string(buff+2,(uint) (buff_ptr - buff)-2));
+      }
       // For next iteration
       used_tables|=table->map;
       if (result->send_data(item_list))