UPDATE 3-Apple revenue, iPhone sales disappoint; shares dive

* iPhone disappointment spurs fears of slowing growth * Investors worry about 2013 pipeline * Loses $50 bln of market value after hours as shares tank By Poornima Gupta SAN FRANCISCO, Jan 23 (Reuters) - Apple Inc missed Wall Street's revenue forecast for the third straight quarter as iPhone sales came in below expectations, fueling investors' worries that its dominance of the mobile industry was slipping. Shares of the world's largest tech company fell 10 percent to $463 a