Query_cache::send_result_to_client() may corrupt THD::query_plan_flags

/mariadb/5.5/sql/log_slow.h:30:36: warning: left shift of negative value [-Wshift-negative-value]

#define QPLAN_QC_NO           1 << 6

                                   ^

/mariadb/5.5/sql/sql_cache.cc:2084:52: note: in expansion of macro 'QPLAN_QC_NO'

   thd->query_plan_flags= (thd->query_plan_flags & ~QPLAN_QC_NO) | QPLAN_QC;