Don't assert that values fit in 32 bits if the NDR64 flag is set.

For now, this just pacifies fuzz-testing.  If real world examples have this, there needs to be a drastic overhaul to support fields that could be either 32 or 64-bit values.

Bug:9329
Change-Id: I3e28808ca0291868a5f84258b0ee1e2a922703c2
Reviewed-on: https://code.wireshark.org/review/4189
Reviewed-by: Michael Mann <mmann78@netscape.net>