ddns.cgi: Support hostname details without seperating dots.

ddns.cgi: Support hostname details without seperating dots.

To keep compatiblity with the settings file of the old DDNS update script
(setddns.pl) we keept the storrage of the hostname information in
two parts (hostname and domain) and connected both with a dot to get a valid
FQDN again. OpenDNS and may some other providers do not use a dotted format
for this information, so one of these two values were empty.

We now can handle such cases in a right way.