update_next_aext() could possibly rewrite values in elen and eloc, possibly
leading to data corruption when rewriting a file.  Use temporary variables
instead.  Also advance cur_epos as it can also point to an indirect extent
pointer.
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>