jfs: Add missing NULL pointer check in __get_metapage

alloc_metapage can return a NULL pointer so check for that.
Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

fs/jfs/jfs_metapage.c

@@ -663,6 +663,8 @@ struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
 	} else {
 		INCREMENT(mpStat.pagealloc);
 		mp = alloc_metapage(GFP_NOFS);
+		if (!mp)
+			goto unlock;
 		mp->page = page;
 		mp->sb = inode->i_sb;
 		mp->flag = 0;