SAN DIEGO — San Diego recently netted its first conviction under the city’s ordinance barring anyone from having ghost guns, the City Attorney’s Office said Friday. A 23-year-old man pleaded guilty last month to three misdemeanor charges linked to a December incident in which he tossed the gun as he ran from police, the office said in a news release. His arrest happened two months after an ordinance banning possession of the non-serialized guns went into effect. Ghosts guns are do-it-yourself firearms assembled by hand from parts that often come in prepackaged kits. Because the parts — like an…