fix returned value type for empty json objects

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

mysql-test/main/statistics_json.result

@@ -101,7 +101,7 @@ ERROR HY000: Failed to parse histogram, encountered JSON_TYPE '1'.
 UPDATE mysql.column_stats SET histogram='{}' WHERE table_name='t1';
 FLUSH TABLES;
 SELECT * FROM t1;
-ERROR HY000: Failed to parse histogram, encountered JSON_TYPE '32641'.
+ERROR HY000: Failed to parse histogram, encountered JSON_TYPE '1'.
 DELETE FROM mysql.column_stats;
 DROP TABLE t1;
 create schema world;

sql/sql_statistics.cc

@@ -1993,11 +1993,10 @@ bool json_get_array_items(const char *json, const char *json_end, int *value_typ
 
   json_scan_start(&je, &my_charset_utf8mb4_bin, (const uchar *)json, (const uchar *)json_end);
 
-  if (json_read_value(&je) || je.value_type != JSON_VALUE_ARRAY)
+  if (json_read_value(&je) || (*value_type = je.value_type) != JSON_VALUE_ARRAY)
   {
     return false;
   }
-  *value_type = je.value_type;
 
   std::string val;
   while(!json_scan_next(&je))