Don't generate code if typemap is unavailable

[Gurpartap]

^

[natefinch]

So, I actually don't think this is valid. The typemap is technically optional. If your templates don't need .Type, you don't need the typemap (like if you're generating docs about the database schema or something).

It might be worth a warning if you run with -v or something... but we shouldn't fail.

[Gurpartap]

My aim with this issue was to not allow generation of invalid code. Perhaps it is the template's responsibility to ensure this.