inform test result of zero hist_size for json histogram

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

mysql-test/main/statistics_json.result

@@ -19,7 +19,7 @@ test.t1	analyze	status	Engine-independent statistics collected
 test.t1	analyze	status	OK
 SELECT * FROM mysql.column_stats WHERE table_name='t1';
 db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency	hist_size	hist_type	histogram
-test	t1	a	1	25	0.0000	4.0000	1.0000	10	JSON	[
+test	t1	a	1	25	0.0000	4.0000	0.0000	10	JSON	[
   "3",
   "5",
   "7",
@@ -31,7 +31,7 @@ test	t1	a	1	25	0.0000	4.0000	1.0000	10	JSON	[
   "21",
   "23"
 ]
-test	t1	b	1	9	0.0000	1.6400	1.0000	10	JSON	[
+test	t1	b	1	9	0.0000	1.6400	0.0000	10	JSON	[
   "11",
   "13",
   "15",
@@ -43,7 +43,7 @@ test	t1	b	1	9	0.0000	1.6400	1.0000	10	JSON	[
   "5",
   "7"
 ]
-test	t1	c	1	9	0.0000	2.0000	1.0000	10	JSON	[
+test	t1	c	1	9	0.0000	2.0000	0.0000	10	JSON	[
   "11",
   "13",
   "15",
@@ -55,7 +55,7 @@ test	t1	c	1	9	0.0000	2.0000	1.0000	10	JSON	[
   "5",
   "7"
 ]
-test	t1	d	1	25	0.0000	8.0000	1.0000	10	JSON	[
+test	t1	d	1	25	0.0000	8.0000	0.0000	10	JSON	[
   "3",
   "5",
   "7",

sql/sql_statistics.cc

@@ -1283,7 +1283,6 @@ void Histogram_json::init_for_collection(MEM_ROOT *mem_root, Histogram_type htyp
 
 bool Histogram_json::parse(MEM_ROOT *mem_root, Histogram_type type_arg, const uchar *ptr, uint size_arg)
 {
-  size = (uint8) size_arg;
   type = type_arg;
   // I think we could use memcpy here, but not sure about how to get the right size
   // since we can't depend on size_arg (it's zero for json histograms)
@@ -1303,7 +1302,7 @@ bool Histogram_json::parse(MEM_ROOT *mem_root, Histogram_type type_arg, const uc
 
 void Histogram_json::serialize(Field *field)
 {
-  field->store((char*)get_values(), strlen((char*)get_values()),
+  field->store((char*)values, strlen((char*)values),
                &my_charset_bin);
 }
 

sql/sql_statistics.h

@@ -372,9 +372,9 @@ class Histogram_json : public Histogram_base
            is_available();
   }
 
-  void set_values (uchar *vals) override { values= (uchar *) vals; }
+  void set_values (uchar *vals) override { values= vals; }
 
-  uchar *get_values() override { return (uchar *) values; }
+  uchar *get_values() override { return values; }
 
   double range_selectivity(double min_pos, double max_pos) override {return 0.1;}