network/nexthop: do not share NextHop.nexthops and NextHop.routes with duplicated object

Otherwise, these may be freed twice.
But, fortunately, when this function is called, both are NULL.
So, this should not change any behavior. But for safety.

src/network/networkd-nexthop.c

@@ -261,6 +261,8 @@ static int nexthop_dup(const NextHop *src, NextHop **ret) {
         dest->network = NULL;
         dest->section = NULL;
         dest->group = NULL;
+        dest->nexthops = NULL;
+        dest->routes = NULL;
 
         HASHMAP_FOREACH(nhg, src->group) {
                 _cleanup_free_ struct nexthop_grp *g = NULL;