asan: _bfd_pei_slurp_codeview_record use of uninit value

Fixes some seriously careless code.  bfd_bread return value is
(bfd_size_type)-1 on error.  "if (bfd_bread (...) < 4)" does not check
for an error since bfd_size_type is unsigned.  In any case, I think we
should be reading and checking the requested length.

	* peXXigen.c (_bfd_XXi_slurp_codeview_record): Properly check
	return value of bfd_bread.  Don't read more than requested length.
	Sanity check length.  Properly terminate file name.