LOS ANGELES (Reuters) - Jennifer Lopez is casting doubt on whether she will return to "American Idol" next year as she juggles motherhood with a comeback in both her pop music and acting careers. Lopez, who has young twins, told talk show host Ellen DeGeneres this week that she wasn't sure about renewing her contract as a judge on the TV singing contest for a third year. And on Wednesday, sources close to the singer told E! News that she was "just too busy" and was planning on calling an end to her time on "American Idol". "Now this is my second year - I don't know if I can go for a third ...