Michael Brown
0620429785
[pxe] Avoid touching fields that may not exist in PXENV_UNDI_GET_NIC_TYPE
Earlier versions of the PXE specification do not have the SubVendor_ID
and SubDevice_ID fields, and some NBPs may not provide space for them.
Avoid overwriting the contents of these fields, just in case.
This is similar to the problem with the BufferLimit field in
PXENV_GET_CACHED_INFO.
Signed-off-by: Michael Brown <mcb30@ipxe.org>