fixed clearing the end of extents when extracting metadata

When extracting the metadata, unused data at the end of MFT records is
supposed to be cleared. This was done for the base record of each file,
but not for the extent records.

ntfsprogs/ntfsclone.c

@@ -1407,8 +1407,13 @@ static int walk_clusters(ntfs_volume *volume, struct ntfs_walk_cluster *walk)
 		walk->image->ni = ni;
 		walk_attributes(walk);
 out:
-		if (wipe) {
+		if (wipe && !opt.metadata_image) {
+			int i;
+
 			wipe_unused_mft_data(ni);
+			for (i = 0; i < ni->nr_extents; ++i) {
+				wipe_unused_mft_data(ni->extent_nis[i]);
+			}
 			mft_inode_write_with_same_usn(volume, ni);
 		}