Fixed main.create-big failure

After MDEV-17772 table existence check is performed much earlier, so
create_table_select_before_check_if_exists debug sync point is not
reachable when table exists.

Moved debug sync point to appropriate place.

mysql-test/main/create-big.result

@@ -237,11 +237,11 @@ select @a;
 @a
 0
 drop table t1;
-set debug_sync='create_table_select_before_check_if_exists SIGNAL parked WAIT_FOR go';
-create table if not exists t1 select 1 as i;;
+set debug_sync='create_table_before_check_if_exists SIGNAL parked WAIT_FOR go';
+create table if not exists t1 select 1 as i;
 connection addconroot1;
 set debug_sync='now WAIT_FOR parked';
-drop table t1;;
+drop table t1;
 connection addconroot2;
 set debug_sync='now SIGNAL go';
 connection default;
@@ -249,11 +249,11 @@ connection addconroot1;
 connection default;
 create table t1 (i int);
 set @a:=0;
-set debug_sync='create_table_select_before_check_if_exists SIGNAL parked WAIT_FOR go';
-create table if not exists t1 select 1 as i;;
+set debug_sync='create_table_before_check_if_exists SIGNAL parked WAIT_FOR go';
+create table if not exists t1 select 1 as i;
 connection addconroot1;
 set debug_sync='now WAIT_FOR parked';
-create trigger t1_bi before insert on t1 for each row set @a:=1;;
+create trigger t1_bi before insert on t1 for each row set @a:=1;
 connection addconroot2;
 set debug_sync='now SIGNAL go';
 connection default;

mysql-test/main/create-big.test

@@ -395,11 +395,11 @@ select @a;
 drop table t1;
 
 # Concurrent DROP TABLE
-set debug_sync='create_table_select_before_check_if_exists SIGNAL parked WAIT_FOR go';
---send create table if not exists t1 select 1 as i;
+set debug_sync='create_table_before_check_if_exists SIGNAL parked WAIT_FOR go';
+--send create table if not exists t1 select 1 as i
 connection addconroot1;
 set debug_sync='now WAIT_FOR parked';
---send drop table t1;
+--send drop table t1
 connection addconroot2;
 # Wait until the above DROP TABLE is blocked due to CREATE TABLE
 let $wait_condition=
@@ -417,11 +417,11 @@ connection default;
 # Concurrent CREATE TRIGGER
 create table t1 (i int);
 set @a:=0;
-set debug_sync='create_table_select_before_check_if_exists SIGNAL parked WAIT_FOR go';
---send create table if not exists t1 select 1 as i;
+set debug_sync='create_table_before_check_if_exists SIGNAL parked WAIT_FOR go';
+--send create table if not exists t1 select 1 as i
 connection addconroot1;
 set debug_sync='now WAIT_FOR parked';
---send create trigger t1_bi before insert on t1 for each row set @a:=1;
+--send create trigger t1_bi before insert on t1 for each row set @a:=1
 connection addconroot2;
 # Wait until the above DROP TABLE is blocked due to CREATE TABLE
 let $wait_condition=

sql/sql_base.cc

@@ -3893,6 +3893,7 @@ static bool upgrade_lock_if_not_exists(THD *thd,
   if (thd->lex->sql_command == SQLCOM_CREATE_TABLE ||
       thd->lex->sql_command == SQLCOM_CREATE_SEQUENCE)
   {
+    DEBUG_SYNC(thd,"create_table_before_check_if_exists");
     if (!create_info.or_replace() &&
         ha_table_exists(thd, &create_table->db, &create_table->table_name))
     {

sql/sql_insert.cc

@@ -4420,8 +4420,6 @@ select_create::prepare(List<Item> &_values, SELECT_LEX_UNIT *u)
     thd->binlog_start_trans_and_stmt();
   }
 
-  DEBUG_SYNC(thd,"create_table_select_before_check_if_exists");
-
   if (!(table= create_table_from_items(thd, &values, &extra_lock, hook_ptr)))
     /* abort() deletes table */
     DBUG_RETURN(-1);