A 15-year-old boy was arrested for the death of his friend and fellow gangbanger after the suspect’s gun went off while he was flashing it inside a Queens apartment Wednesday afternoon, police and sources said. Jamuri Mezar, 14, was shot and killed in his Jamaica home at the Norman Towers during what law enforcement sources described as an accidental discharge. The older teen brought a stolen 9mm gun to Mezar’s home and was showing it off when it fired, striking Mezar in the head, the sources said. Mezar was pronounced dead on scene, police said. His pal bolted from the...