Moments ago, WarnerMedia and Discovery were popping preliminary champagne bottles as the media mega merger edged one step closer to completion. This is a lesson in why one should never celebrate too soon, as things can change in the blink of an eye in this industry, with the deal now on a potential collision course, according to the red flags adorning AT&T’s latest 10K filing. “The proposed separation and combination of our WarnerMedia business with Discovery may not be completed on the currently contemplated timeline or at all,” reads the first stinging statement to catch our eye. As we reported two weeks ago, the transaction is expected to close next quarter, following regulatory approval of the merged Warner Bros. Discovery…