[Patch] Empty Membuf terminate

Hi all,

When an error page template file is empty I am getting strange
behaviour, sometimes I am getting an assertion failed, some other cases
crap send to the client instead of an error page.

These problems caused because a MemBuf , in which no data added is not
NULL terminated. I am attaching a patch which terminates an empty MemBuf.
We are consider MemBuf as always NULL terminated, so I believe we must
terminate an empty MemBuf too.

Regards,
   Christos