I go to the roof to pick up the sniper rifle and get the "donk" sound like I've collected it but it remains in place uncollected. The map shows I still need to pick it up. I then switch to the one I have because I dailed a number to arm myself with one. I then wait for ever for something to happen with the drug deal and it never does. Packie never ends up in a fight. Is this because I've cheated my way to the sniper rifle earlier or am I missing something obvious/simple (entirely possible), like waiting longer than the ten minutes I've given it. If my cheating has blocked this mission how do I go back and complete it the right way?