Avoid possible race condition in accessing slave statistics

during shutdown. (Bug #11796)

sql/sql_show.cc

@@ -1890,7 +1890,7 @@ int mysqld_show(THD *thd, const char *wild, show_var_st *variables,
       case SHOW_SLAVE_RUNNING:
       {
 	pthread_mutex_lock(&LOCK_active_mi);
-	end= strmov(buff, (active_mi->slave_running &&
+	end= strmov(buff, (active_mi && active_mi->slave_running &&
 			   active_mi->rli.slave_running) ? "ON" : "OFF");
 	pthread_mutex_unlock(&LOCK_active_mi);
 	break;
@@ -1902,9 +1902,12 @@ int mysqld_show(THD *thd, const char *wild, show_var_st *variables,
           SLAVE STATUS, and have the sum over all lines here.
         */
 	pthread_mutex_lock(&LOCK_active_mi);
+        if (active_mi)
+        {
           pthread_mutex_lock(&active_mi->rli.data_lock);
           end= int10_to_str(active_mi->rli.retried_trans, buff, 10);
           pthread_mutex_unlock(&active_mi->rli.data_lock);
+        }
 	pthread_mutex_unlock(&LOCK_active_mi);
 	break;
       }