Fix #59—Fix crash when using nil title or message
Fix #59—Fix crash when using nil title or message

sberrevoets/SDCAlertView,Wurrly/SDCAlertView,sberrevoets/SDCAlertView,adamkaplan/SDCAlertView,winkapp/SDCAlertView,DeskConnect/SDCAlertView,Nykho/SDCAlertView,HuylensHu/SDCAlertView,DeskConnect/SDCAlertView