ndrdump: check bounds when passed functions/structs by integer

ndrdump: check bounds when passed functions/structs by integer

The function or struct number should be >= 0 ans the underlying
number it is compared to is uint32_t.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14191

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Pair-programmed-with: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>

Autobuild-User(master): Douglas Bagnall <dbagnall@samba.org>
Autobuild-Date(master): Wed Nov 13 01:55:33 UTC 2019 on sn-devel-184