One company's negative results can increase scrutiny of another's work.When one player stumbles in a high-stakes competition, it's often to the glee of the other contenders. In mid-June, Pfizer's (PFE -0.86%) gene-therapy candidate to treat Duchenne muscular dystrophy (DMD) didn't hit the mark in a late-stage clinical trial; it'd be logical to assume that shares of Sarepta Therapeutics, (SRPT -1.64%) a biotech focused on developing DMD drugs, would then rise.But that didn't happen -- at least not until Sare ...