In order to take advantage of padding, and to avoid rewriting the
entire file, remove the tags before setting them again in the 'update'
command. If the new title is not longer than the previous one, the file
will not be rewritten.

The 'clean' command still needs to be run afterwards, and will remove
the padding if present.

Signed-off-by: Cédric Marie <cedric@hjuvi.lautre.net>