Sir Ian McKellen fears each script or acting offer he gets may turn out to be his “last job”. ‘The Lord of the Rings’ acting veteran, who turned 85 in May, says his mortality is on his mind so much he now only takes work he knows will be quality in case he shuffles off after it’s done. He told The Times: “You are aware that this life doesn’t go on for ever. “If you want to know that you are mortal you just have to look at your address book. “And so when a script comes through, or the hint of an offer, you think, ‘This might be my last job. No. I’m not doing that.’” Ian is now playing hard-livi…