netowrkd:deserialize_dhcp_routes verify strndup ret

strndup need to be chcked

src/libsystemd-network/network-internal.c

@@ -474,6 +474,8 @@ int deserialize_dhcp_routes(struct sd_dhcp_route **ret, size_t *ret_size, size_t
                         return -ENOMEM;
 
                 entry = strndup(word, len);
+                if(!entry)
+                        return -ENOMEM;
 
                 tok = entry;