If you get +2 to either Dex or Cha, and you're using a 22 point buy, you can afford the following stat line, which includes a +2 to either Dex or Cha, and no other boosts:
10/11/17/10/8/17
So in a way it doesn't matter much which race you pick, as long as it gives you more than zero on stats.. This is a perfectly viable statline.
The real problem you may encounter, if you're concerned about power level, is that multiclassing a rogue into a warlock doesn't do that much for you. The rogue powers already include both melee and ranged attacks. The warlock powers will grant you different ranged attacks, but they often won't be significantly different. It won't be like multiclassing a warlord into a wizard, where his single target melee attacks get augmented by area of effect explosions, or anything like that.
10/11/17/10/8/17
So in a way it doesn't matter much which race you pick, as long as it gives you more than zero on stats.. This is a perfectly viable statline.
The real problem you may encounter, if you're concerned about power level, is that multiclassing a rogue into a warlock doesn't do that much for you. The rogue powers already include both melee and ranged attacks. The warlock powers will grant you different ranged attacks, but they often won't be significantly different. It won't be like multiclassing a warlord into a wizard, where his single target melee attacks get augmented by area of effect explosions, or anything like that.