Bug#26807 "set global event_scheduler=1" and --skip-grant-tables crashes server

- Crash occured because Event engine is only initialized if
  ACLs are used but not properly marked as disabled.
- The patch is to mark the Event engine as DISABLED if no ACLs
  are used to avoid access of uninitialized variables.


mysql-test/r/skip_grants.result:
  Added test case
mysql-test/t/skip_grants.test:
  Added test case

mysql-test/r/skip_grants.result

@@ -58,3 +58,5 @@ DROP PROCEDURE p3;
 DROP FUNCTION f1;
 DROP FUNCTION f2;
 DROP FUNCTION f3;
+set global event_scheduler=1;
+ERROR HY000: The MySQL server is running with the --event-scheduler=DISABLED or --skip-grant-tables option so it cannot execute this statement

mysql-test/t/skip_grants.test

@@ -108,3 +108,10 @@ DROP PROCEDURE p3;
 DROP FUNCTION f1;
 DROP FUNCTION f2;
 DROP FUNCTION f3;
+
+#
+# Bug #26807 "set global event_scheduler=1" and --skip-grant-tables crashes server
+#
+--error ER_OPTION_PREVENTS_STATEMENT
+set global event_scheduler=1;
+

sql/mysqld.cc

@@ -3691,6 +3691,7 @@ we force server id to 2, but this MySQL server will not act as a slave.");
     udf_init();
 #endif
   }
+
   init_status_vars();
   if (opt_bootstrap) /* If running with bootstrap, do not start replication. */
     opt_skip_slave_start= 1;
@@ -3737,6 +3738,10 @@ we force server id to 2, but this MySQL server will not act as a slave.");
     if (Events::get_instance()->init())
       unireg_abort(1);
   }
+  else
+  {
+    Events::opt_event_scheduler = Events::EVENTS_DISABLED; 
+  }
 
   /* Signal threads waiting for server to be started */
   pthread_mutex_lock(&LOCK_server_started);

sql/set_var.cc

@@ -3990,7 +3990,7 @@ sys_var_event_scheduler::update(THD *thd, set_var *var)
   DBUG_ENTER("sys_var_event_scheduler::update");
   if (Events::opt_event_scheduler == Events::EVENTS_DISABLED)
   {
-    my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0), "--event-scheduler=DISABLED");
+    my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0), "--event-scheduler=DISABLED or --skip-grant-tables");
     DBUG_RETURN(TRUE);
   }