asan: alpha-vms: Heap-buffer-overflow

asan: alpha-vms: Heap-buffer-overflow

This fixes yet more errors in the alpha-vms buffer size checks.

	* vms-alpha.c (_bfd_vms_slurp_eisd): Don't overflow when checking
	offset.  Don't overflow when checking rec_size, and do allow
	rec_size to the end of the buffer.  Ensure eisd->type can be
	accessed, not just the first 32 bytes.  Don't call
	_bfd_vms_save_counted_string with zero length remaining.  Fail
	on empty string section name.
	(_bfd_vms_slurp_egsd): Formatting.  Catch more reads past end
	of record size.  Correct remaining length calculation.  Fail
	on empty string section name.  Consolidate error paths.