WASHINGTON—A federal judge on Tuesday declared a mistrial in the government’s embezzlement case against Michael Avenatti, giving the already convicted celebrity lawyer a temporary reprieve as he defends against a slew of criminal charges. U.S. District Judge James Selna in Santa Ana, California, said Avenatti was entitled to a new trial because prosecutors had failed to turn over relevant billing-related evidence. Avenatti, 50, who is representing himself, had argued that the evidence might be exculpatory, and that the failure to turn it over undermined his ability to mount a defense. The mistrial was confirmed in an email from the office of Acting U.S. Attorney Tracy Wilkison in Los Angeles. Selna found no evidence of intentional misconduct by prosecutors, according to The Recorder and Law360. He set a tentative Oct. 12 date for another trial, but Avenatti may argue he cannot be retried because of double jeopardy. The trial had lasted …