[Gameplay] Sightstone refill zone does not match heal/buy

When walking back to the fountain, the distance that you can buy/heal at is larger than the distance you need to be to refill sightstone.

1. Buy sightstone
2. Leave fountain
3. Use at least 1 sightstone ward
4. Walk towards fountain until you are just close enough to buy/heal - sighstone does not refill until you take another few steps.

There is no apparent reason for sighstone refill not to match the buy zone - sometimes when I walk back to the fountain I end up back in lane not realizing that sightstone did not refill.