sd-netlink: add several assertions

src/libsystemd/sd-netlink/netlink-socket.c

@@ -244,7 +244,8 @@ int socket_writev_message(sd_netlink *nl, sd_netlink_message **m, size_t msgcoun
         size_t i;
 
         assert(nl);
-        assert(msgcount);
+        assert(m);
+        assert(msgcount > 0);
 
         iovs = new0(struct iovec, msgcount);
         if (!iovs)

src/libsystemd/sd-netlink/sd-netlink.c

@@ -237,6 +237,7 @@ int sd_netlink_sendv(sd_netlink *nl,
         assert_return(nl, -EINVAL);
         assert_return(!rtnl_pid_changed(nl), -ECHILD);
         assert_return(messages, -EINVAL);
+        assert_return(msgcount > 0, -EINVAL);
 
         if (ret_serial) {
                 serials = new0(uint32_t, msgcount);