fs/ntfs3: Fix possible NULL-ptr-deref in ni_readpage_cmpr()

Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

fs/ntfs3/frecord.c

@@ -2148,7 +2148,7 @@ int ni_readpage_cmpr(struct ntfs_inode *ni, struct page *page)
 
 	for (i = 0; i < pages_per_frame; i++) {
 		pg = pages[i];
-		if (i == idx)
+		if (i == idx || !pg)
 			continue;
 		unlock_page(pg);
 		put_page(pg);