`basic-foreign-type` method fails when `foreign-record-fields` is empty

[igorcalabria]

To reproduce just try to wrap lz4 https://github.com/lz4/lz4/blob/dev/lib/lz4.h

(autowrap:c-include "/usr/include/lz4.h")

I think it might be related to this incomplete typedef here https://github.com/lz4/lz4/blob/dev/lib/lz4.h#L314

Not sure if it's the right fix, but adding a check on https://github.com/rpav/cl-autowrap/blob/master/autowrap/sffi.lisp#L186

  (if (and (foreign-scalar-p type) (foreign-record-fields type))

worked