For many pop stars, headlining an acoustic musical fundraiser after over a year of not performing live may seem like a daunting task. But if Selena Gomez was even the slightest bit nervous when she took to the stage at New York City’s Best Buy Theater on Saturday night for UNICEF’s third annual charity concert, she certainly didn’t let it show. Gomez, who is only 20, has performed at all three of the organization’s annual charity MORE