Would Guttersnipe plus a cyphered card result in an infinite loop of damage?
No, that doesn't amount to an infinite loop, because of this term in cipher's definition:


  Whenever that creature deals combat damage to a player [...]


(That's an extract from the reminder text, but the actual rules definition is virtually identical.)

Combat damage is just the damage dealt during the combat damage step. In other words, it's the damage Guttersnipe would deal if you tapped it to attack, and it wasn't blocked and ended up attacking the player. The damage dealt by Guttersnipe's triggered ability does not count as combat damage, so it doesn't trigger cipher.

Your combo would work if cipher just triggered off any damage at all, in which case it'd say this:


  Whenever that creature deals damage to a player [...]