Add guard in thread_set_priority ensuring priority values are within correct range

src/threads/thread.c

@@ -354,6 +354,7 @@ thread_foreach (thread_action_func *func, void *aux)
 void
 thread_set_priority (int new_priority) 
 {
+  ASSERT (PRI_MIN <= new_priority && new_priority <= PRI_MAX);
   thread_current ()->priority = new_priority;
 }