vms-alpha: ehdr checks

I noticed that _bfd_vms_slurp_ehdr wrongly used buf_size (rather than
rec_size) when sanity checking.

	* vms-alpha.c (_bfd_vms_slurp_ehdr): Don't allow access to
	uninitialised buffer memory.  Tidy code generally, using
	remaining record length for sanity checks.
1 file changed