“A spoonful of sugar makes the medicine go down,” the opening line of a breezy song from a child-friendly movie of yore, sprang to mind when I perused Friday’s (Feb. 8) San Diego Symphony program. An obscure, 30-minute tone poem “Mississippi River Suite” by the nearly forgotten African-American composer Florence Price was the medicine, and Rimsky-Korsakov’s numbingly familiar “Scheherazade” was the spoonful of sugar on Taiwanese conductor Mei-Ann Chen’s prescription for her inaugural appearance on the local podium. Between these two tone poems, the orchestra’s Principal Horn Benjamin Jaber came front and center to give his take on Richard Strauss’…