Fixed valgrind problems of the patch for bug 794901.

sql/sql_derived.cc

@@ -478,11 +478,7 @@ bool mysql_derived_merge_for_insert(THD *thd, LEX *lex, TABLE_LIST *derived)
   if (derived->merged_for_insert)
     return FALSE;
   if (derived->is_materialized_derived())
-  {
-    bool res=  mysql_derived_prepare(thd, lex, derived);
-    derived->select_lex->leaf_tables.push_back(derived);
-    return res;
-  }
+    return mysql_derived_prepare(thd, lex, derived);
   if (!derived->is_multitable())
   {
     if (!derived->updatable)

sql/sql_lex.cc

@@ -1639,6 +1639,7 @@ void st_select_lex::init_query()
   nest_level= 0;
   link_next= 0;
   lock_option= TL_READ_DEFAULT;
+  is_prep_leaf_list_saved= FALSE;
 
   bzero((char*) expr_cache_may_be_used, sizeof(expr_cache_may_be_used));
 }
@@ -1674,7 +1675,6 @@ void st_select_lex::init_select()
   cond_value= having_value= Item::COND_UNDEF;
   inner_refs_list.empty();
   full_group_by_flag= 0;
-  is_prep_leaf_list_saved= FALSE;
   insert_tables= 0;
   merged_into= 0;
 }