From: Jan Kara <jack@ucw.cz>

This patch fixes possible quota files corruption which could happen when root
did not have any inodes&space allocated.

Originally this could not happen as structure would not be written to disk in
that case but with journalled quota we need to write even all-zero structure. 
The fix is not very nice but change of the format on disk is probably worse (I
made a mistake with not including the usage-bitmaps into format :().