Backport of revno: 2617.65.10

Bug #45067 Assertion `stmt_da->is_error()' in 
           Delayed_insert::open_and_lock_table

The assert was triggered when delayed insert was killed by another 
connection using mysql_notify_thread_having_shared_lock().
During handling of thd->killed, thd.fatal_error() was called without
a previous call to my_error() which triggered the assert.
This patch allows the assert to pass if thd->killed has been set.

sql/sql_class.h

@@ -2216,7 +2216,7 @@ public:
   */
   inline void fatal_error()
   {
-    DBUG_ASSERT(main_da.is_error());
+    DBUG_ASSERT(stmt_da->is_error() || killed);
     is_fatal_error= 1;
     DBUG_PRINT("error",("Fatal error set"));
   }