Field data for a query was stored to the stmt->alloc that is emptied
with mysql_stmt_close statement only. That means a lot of memory can
be occupied without a reason if used doesn't call mysql_stmt_close often.


libmysql/libmysql.c:
  Bug #33796 Memory leak for prepared statements in embedded server.
  
  Clean up result->alloc even if there's no 'data' created
libmysqld/lib_sql.cc:
  Bug #33796 Memory leak for prepared statements in embedded server.
  
  alloc 'fields' in the 'result.alloc' as the 'mem_root' is only cleaned with
  mysql_stmt_close'