libctf, types: ints, floats and typedefs with no name are invalid

libctf, types: ints, floats and typedefs with no name are invalid

Report them as such, rather than letting ctf_decl_sprintf wrongly
conclude that the printing of zero characters means we are out of
memory.

libctf/
	* ctf-types.c (ctf_type_aname): Return ECTF_CORRUPT if
	ints, floats or typedefs have no name.  Fix comment typo.