NTFS: Fix handling of valid but empty mapping pairs array in

fs/ntfs/runlist.c::ntfs_mapping_pairs_decompress().

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>

fs/ntfs/ChangeLog

@@ -46,6 +46,8 @@ ToDo/Notes:
 	- Fix two nasty runlist merging bugs that had gone unnoticed so far.
 	  Thanks to Stefano Picerno for the bug report.
 	- Remove two bogus BUG_ON()s from fs/ntfs/mft.c.
+	- Fix handling of valid but empty mapping pairs array in
+	  fs/ntfs/runlist.c::ntfs_mapping_pairs_decompress().
 
 2.1.23 - Implement extension of resident files and make writing safe as well as
 	 many bug fixes, cleanups, and enhancements...

fs/ntfs/runlist.c

@@ -760,6 +760,9 @@ runlist_element *ntfs_mapping_pairs_decompress(const ntfs_volume *vol,
 		ntfs_error(vol->sb, "Corrupt attribute.");
 		return ERR_PTR(-EIO);
 	}
+	/* If the mapping pairs array is valid but empty, nothing to do. */
+	if (!vcn && !*buf)
+		return old_rl;
 	/* Current position in runlist array. */
 	rlpos = 0;
 	/* Allocate first page and set current runlist size to one page. */