Fix memory leak in bfd_get_debug_link_info_1

Fix memory leak in bfd_get_debug_link_info_1

	* opncls.c (bfd_get_alt_debug_link_info): Don't bother freeing
	after bfd_malloc_and_get_section failure.
	(get_build_id): Likewise.
	(bfd_get_debug_link_info_1): Likewise.  Free section contents
	when crc not present.
	* section.c (bfd_malloc_and_get_section): Document that the
	buffer is NULL on error return.