By Maxx Chatsko Social media is speculating about the idea that Exact Sciences would buy Invitae. Investors should pinch themselves out of the daydream. One of the most important lessons of the stock-market correction is that the power of positive thinking can take investors only so far. For the shareholders of Invitae (NVTA) – Get Invitae Corporation Report, it could lead to more pain and suffering. As shares of the genetic-testing business flounder, some investors expect a larger peer, like Exact Sciences (EXAS) – Get Exact Sciences Corporation Report, to swoop in and acquire Invitae on the …