f2fs: don't set cached_en if it will be freed

If en has empty list pointer, it will be freed sooner, so we don't need to
set cached_en with it.

Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/extent_cache.c

···
 	if (en) {
 		*ei = en->ei;
 		spin_lock(&sbi->extent_lock);
-		if (!list_empty(&en->list))
+		if (!list_empty(&en->list)) {
 			list_move_tail(&en->list, &sbi->extent_list);
-		et->cached_en = en;
+			et->cached_en = en;
+		}
 		spin_unlock(&sbi->extent_lock);
 		ret = true;
 	}
···
 		return NULL;
 
 	__try_update_largest_extent(et, en);
-	et->cached_en = en;
 
 	spin_lock(&sbi->extent_lock);
-	if (!list_empty(&en->list))
+	if (!list_empty(&en->list)) {
 		list_move_tail(&en->list, &sbi->extent_list);
+		et->cached_en = en;
+	}
 	spin_unlock(&sbi->extent_lock);
 	return en;
 }
···
 		return NULL;
 
 	__try_update_largest_extent(et, en);
-	et->cached_en = en;
 
 	/* update in global extent list */
 	spin_lock(&sbi->extent_lock);
 	list_add_tail(&en->list, &sbi->extent_list);
+	et->cached_en = en;
 	spin_unlock(&sbi->extent_lock);
 	return en;
 }