[Kernel] Fix the critical issue when scheduler not start

src/scheduler.c

@@ -884,14 +884,17 @@ void rt_exit_critical(void)
     level = rt_hw_interrupt_disable();
 
     rt_scheduler_lock_nest --;
-
     if (rt_scheduler_lock_nest <= 0)
     {
         rt_scheduler_lock_nest = 0;
         /* enable interrupt */
         rt_hw_interrupt_enable(level);
 
-        rt_schedule();
+        if (rt_current_thread)
+        {
+            /* if scheduler is started, do a schedule */
+            rt_schedule();
+        }
     }
     else
     {