Fix potential address violations when processing a corrupt Alpha VMA binary.

Fix potential address violations when processing a corrupt Alpha VMA binary.

	PR binutils/21589
	* vms-alpha.c (_bfd_vms_get_value): Add an extra parameter - the
	maximum value for the ascic pointer.  Check that name processing
	does not read beyond this value.
	(_bfd_vms_slurp_etir): Add checks for attempts to read beyond the
	end of etir record.