Fix crash in demo app on simulating incoming audio message (#1542)
Fix crash in demo app on simulating incoming audio message (#1542)

closes #1541
sebastianludwig/JSQMessagesViewController,preeo/JSQMessagesViewController,preeo/JSQMessagesViewController,derekjcarter/JSQMessagesViewController,jessesquires/JSQMessagesViewController,sebastianludwig/JSQMessagesViewController,cheskapac/JSQMessagesViewController,perpetio/JSQMessagesViewController,TeletronicsDotAe/JSQMessagesViewController,jessesquires/JSQMessagesViewController,adozenlines/JSQMessagesViewController,TeletronicsDotAe/JSQMessagesViewController,adozenlines/JSQMessagesViewController,cheskapac/JSQMessagesViewController,Lucashuang0802/JSQMessagesViewController,Lucashuang0802/JSQMessagesViewController,Lucashuang0802/JSQMessagesViewController,derekjcarter/JSQMessagesViewController,sebastianludwig/JSQMessagesViewController,perpetio/JSQMessagesViewController,GuyKahlon/JSQMessagesViewController,adozenlines/JSQMessagesViewController,preeo/JSQMessagesViewController,eliburke/JSQMessagesViewController,GianniCarlo/JSQMessagesViewController,derekjcarter/JSQMessagesViewController,perpetio/JSQMessagesViewController,WhisperSystems/JSQMessagesViewController,GianniCarlo/JSQMessagesViewController,WhisperSystems/JSQMessagesViewController,TeletronicsDotAe/JSQMessagesViewController