Fix seg fault objdumping a corrupt binary with an invalid sh_link field.

Fix seg fault objdumping a corrupt binary with an invalid sh_link field.

	PR binutils/20063
	* elf.c (bfd_elf_get_elf_syms): Check for out of range sh_link
	field before accessing sections array.

	* readelf.c (get_32bit_section_headers): Warn if an out of range
	sh_link or sh_info field is encountered.
	(get_64bit_section_headers): Likewise.