fix sem_close unmapping of still-referenced semaphore

Signed-off-by: Nmaweiye <maweiye@huawei.com>

src/thread/sem_open.c

@@ -163,10 +163,12 @@ int sem_close(sem_t *sem)
 	int i;
 	LOCK(lock);
 	for (i=0; i<SEM_NSEMS_MAX && semtab[i].sem != sem; i++);
-	if (!--semtab[i].refcnt) {
-		semtab[i].sem = 0;
-		semtab[i].ino = 0;
+	if (--semtab[i].refcnt) {
+		UNLOCK(lock);
+		return 0;
 	}
+	semtab[i].sem = 0;
+	semtab[i].ino = 0;
 	UNLOCK(lock);
 	munmap(sem, sizeof *sem);
 	return 0;