Fix for a bug #1226.

Happens when braces are used on a single select, which leads
to the uninitialized global parameters structure.

mysql-test/r/subselect.result

@@ -1368,4 +1368,10 @@ insert into t1 values ('tttt');
 select * from t1 where ('a','b')=(select 'a','b' from t1 union select 'a','b' from t1);
 s1
 tttt
+explain (select * from t1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+(select * from t1);
+s1
+tttt
 drop table t1;

mysql-test/t/subselect.test

@@ -931,4 +931,6 @@ create table t1 (s1 char(5));
 select (select 'a','b' from t1 union select 'a','b' from t1) from t1;
 insert into t1 values ('tttt');
 select * from t1 where ('a','b')=(select 'a','b' from t1 union select 'a','b' from t1);
+explain (select * from t1);
+(select * from t1);
 drop table t1;

sql/sql_yacc.yy

@@ -2012,8 +2012,9 @@ select_init:
 	    YYABORT;
 	  }
             /* select in braces, can't contain global parameters */
-            sel->master_unit()->global_parameters=
-               sel->master_unit()->fake_select_lex;
+	    if (sel->master_unit()->fake_select_lex)
+              sel->master_unit()->global_parameters=
+                 sel->master_unit()->fake_select_lex;
           } union_opt;
 
 select_init2: