DUBAI, May 20 (Reuters) - Here are some factors that may affect Middle East stock markets on Tuesday. Reuters has not verified the press reports and does not vouch for their accuracy.INTERNATIONAL/REGIONAL* GLOBAL MARKETS-Asian shares inch down, dollar steadiesMKTS/GLOB* Brent steady above $109 on Libya unrest; U.S. crude stocks seen rising O/R* MIDEAST STOCKS-Dubai in biggest drop in 8 mths, most