Dear Maintainer,

I have filed a few bug reports recently by running reportbug on a non-debian
system. This resulted in the subject line of the report email being blank and
the title of the bug report being set to "(no subject)".

The problem occurs because the scripts rely on the existence of the file
`/etc/dpkg/origins/debian` to provide the `type` for that default `SYSTEM`, or
for some other source to provide the `type` for other `SYSTEM`s such as
`"ubuntu"` or `"guug"`, or for the `type` to be set as a command line argument.

There are a few places that a default `type` could be defined. For the attached
patch I chose to apply a global default, although it may be preferable to
instead put per-`SYSTEM` defaults in `debbugs.py`'s definition of `SYSTEMS`.

This bug report is being filed with `reportbug` using this patch, on a system
previously affected by the bug. If all goes well, it will be titled as follows:

reportbug: Missing report type results in Subject being dropped