libctf: unidentified type kinds on open are a sign of file corruption

If we see a CTF type with a kind we do not recognize in its ctt_info
during opening, we cannot skip it and continue opening the file: if the
type kind is unknown, we do not know how long its vlen is, and we cannot
have skipped past it: so if we continue reading we will almost certainly
read in part of the vlen as if it were a new ctf_type_t.

Avoid this trouble by considering unknown type kinds to be a reason to
return ECTF_CORRUPT, just like everything else that reads in type kinds
does.

libctf/
	* ctf-open.c (ctf_types): Fail when unidentified type kinds are
	seen.