Investors who were worried about it should feel confident pressing the buy button.Chipotle Mexican Grill (CMG 0.90%) investors have been on edge since the announcement of the departure of powerhouse CEO Brian Niccol in August. The stock fell after its split in June, and it's tentatively making its way back up as investors get comfortable with the idea that the chain can go on even without Niccol leading the way.If the market had any more quibbles with that notion, the company just made it clear that it's no ...