way back in July, in r.75706, a fix was made ot the strftime usages, which was good...

way back in July, in r.75706, a fix was made ot the strftime usages, which was good, but in this case, the check for a nil time was accidentally removed, and now it is restored, to keep timevals like '1969-12-31 17:00:00' from showing up in the cdrs. No idea what databases will do with this. No bugs filed as yet, but it felt like a bug.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@107019 65c4cc65-6c06-0410-ace0-fbb531ad65f3