count(distint) on an empty table crash fixed

.bzrignore

@@ -523,3 +523,5 @@ vio/test-sslclient
 vio/test-sslserver
 vio/viotest-ssl
 extra/mysql_waitpid
+support-files/MacOSX/Description.plist
+support-files/MacOSX/Info.plist

mysql-test/r/count_distinct.result

@@ -48,3 +48,8 @@ select t1.f1,count(distinct t2.f2),count(distinct 1,NULL) from t1 left join t2 o
 f1	count(distinct t2.f2)	count(distinct 1,NULL)
 1	0	0
 drop table t1,t2;
+create table t1 (f int);
+select count(distinct f) from t1;
+count(distinct f)
+0
+drop table t1;

mysql-test/t/count_distinct.test

@@ -43,3 +43,12 @@ insert into t1 values (1);
 create table t2 (f1 int,f2 int);
 select t1.f1,count(distinct t2.f2),count(distinct 1,NULL) from t1 left join t2 on t1.f1=t2.f1 group by t1.f1;
 drop table t1,t2;
+
+
+#
+# Empty tables
+#
+create table t1 (f int);
+select count(distinct f) from t1;
+drop table t1;
+

sql/item_sum.cc

@@ -918,7 +918,7 @@ int dump_leaf(byte* key, uint32 count __attribute__((unused)),
 }
 
 
-Item_sum_count_distinct::~Item_sum_count_distinct()
+void Item_sum_count_distinct::no_rows_in_result()
 {
   if (table)
     free_tmp_table(current_thd, table);
@@ -927,7 +927,6 @@ Item_sum_count_distinct::~Item_sum_count_distinct()
     delete_tree(&tree);
 }
 
-
 bool Item_sum_count_distinct::fix_fields(THD *thd,TABLE_LIST *tables)
 {
   if (Item_sum_num::fix_fields(thd,tables) ||

sql/item_sum.h

@@ -185,7 +185,8 @@ class Item_sum_count_distinct :public Item_sum_int
     :Item_sum_int(list),table(0),used_table_cache(~(table_map) 0),
      tmp_table_param(0),use_tree(0),always_null(0)
   { quick_group=0; }
-  ~Item_sum_count_distinct();
+  ~Item_sum_count_distinct() { no_rows_in_result(); }
+
   table_map used_tables() const { return used_table_cache; }
   enum Sumfunctype sum_func () const { return COUNT_DISTINCT_FUNC; }
   void reset();
@@ -195,6 +196,7 @@ class Item_sum_count_distinct :public Item_sum_int
   void update_field(int offset) { return ; }	// Never called
   const char *func_name() const { return "count_distinct"; }
   bool setup(THD *thd);
+  void no_rows_in_result();
   unsigned int size_of() { return sizeof(*this);}
 };