fs/ntfs3: Check 'folio' pointer for NULL

It can be NULL if bmap is called.

Fixes: 82cae269 ("fs/ntfs3: Add initialization of super block")
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

fs/ntfs3/inode.c

@@ -571,13 +571,18 @@ static noinline int ntfs_get_block_vbo(struct inode *inode, u64 vbo,
 	clear_buffer_uptodate(bh);
 
 	if (is_resident(ni)) {
-		ni_lock(ni);
-		err = attr_data_read_resident(ni, &folio->page);
-		ni_unlock(ni);
-
-		if (!err)
-			set_buffer_uptodate(bh);
+		bh->b_blocknr = RESIDENT_LCN;
 		bh->b_size = block_size;
+		if (!folio) {
+			err = 0;
+		} else {
+			ni_lock(ni);
+			err = attr_data_read_resident(ni, &folio->page);
+			ni_unlock(ni);
+
+			if (!err)
+				set_buffer_uptodate(bh);
+		}
 		return err;
 	}