Fix for using uninitialized memory

MDEV-22073 MSAN use-of-uninitialized-value in
collect_statistics_for_table()

Other things:
innodb.analyze_table was changed to mainly test statistic
collection. Was discussed with Marko.

sql/sql_statistics.cc

@@ -1671,6 +1671,7 @@ public:
   */
   virtual bool add()
   {
+    table_field->mark_unused_memory_as_defined();
     return tree->unique_add(table_field->ptr);
   }