Fix address violation issues encountered when parsing corrupt binaries.

	PR 21840
	* mach-o.c (bfd_mach_o_read_symtab_strtab): Fail if the symtab
	size is -1.
	* nlmcode.h (nlm_swap_auxiliary_headers_in): Replace assertion
	with error return.
	* section.c (bfd_make_section_with_flags): Fail if the name or bfd
	are NULL.
	* vms-alpha.c (bfd_make_section_with_flags): Correct computation
	of end pointer.
	(evax_bfd_print_emh): Check for invalid string lengths.