UDF code is not really ready to handle extents larger that 1GB. This is
the easy way to forbid creating those.

Also truncation code did not count with the case when there are no
extents in the file and we are extending the file.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Adrian Bunk <bunk@stusta.de>