[PATCH] set default owner/group in db.

[PATCH] set default owner/group in db.

This patch fixes a bug where the udev database stored empty strings
for Owner and Group if they were default. This patch stores the default
value into the database if not set otherwise. See example output:

crw-------    1 root     root       4,  65 Jan 16 11:13 ttyS1

P: /class/tty/ttyS1
N: ttyS1
S:
O: root
G: root

This is a bit of a hack. However, until udev supports setting the
o/g values they will be root/root anyway so the database might as
well reflect the truth instead of empty strings.