Don't clobber the thread variable as we use it again. Since it always is NULL

at the end of that loop we guaranteed a crash when this special handling was
triggered.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@23748 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/sem.cpp

@@ -938,8 +938,10 @@ switch_sem_etc(sem_id semToBeReleased, sem_id id, int32 count,
 					B_INTERRUPTED, true);
 			}
 			RELEASE_SEM_LOCK(sSems[slot]);
-			while ((thread = thread_dequeue(&wakeupQueue)) != NULL)
-				scheduler_enqueue_in_run_queue(thread);
+
+			struct thread *wakeupThread;
+			while ((wakeupThread = thread_dequeue(&wakeupQueue)) != NULL)
+				scheduler_enqueue_in_run_queue(wakeupThread);
 
 			// fall through and reschedule since another thread with a higher priority may have been woken up
 		}