You won't get banend for letting a friend play on your account for multiple reasons:
- Dynamic IP's, logging in on a different IP almost every time happens to a lot of players including me. My public IP changes a lot!
- Who says it isn't you playing at your friend's house?
- Riot doesn't care about sharing accounts that much, unless you or your friend is botting, boosting or trading accounts.
- Hacking accounts is super easy, Riot doesn't do anything unless the player who's account got hacked opens a ticket. It's not like Riot actually checks every account that has a login from a weird location. Which means they probably don't have a system to do it automatically and which decreases the chance of a ban by a lot.
Of course I wouldn't recommend 2 players 1 from China and 1 from Europe playing on the same account every day. But as long as it's from the same country I wouldn't worry about it.