The guitarist for the pop-punk band Hawthorne Heights passed away before the group’s show at the 9:30 Club over the weekend. Casey Calvert, 25, was found dead on the band’s tour bus at around 2:30 p.m. on Saturday, parked outside the venue in Northwest D.C. A cause of death has yet to be determined, but Calvert’s bandmates have been quick to defend against speculation that drugs were involved. They posted the following message to their…