The crash in oil prices and the economic fallout from the coronavirus together pose what could be an existential threat for Africa’s largest economy and biggest crude producer. Nigeria, a country of 200 million people, is slashing production faster than any other major oil economy following the precipitous plunge in global prices. Cargo ships full of millions of barrels of Nigerian crude have nowhere to go, with much of the world on lockdown. Nigerian oil companies are desperately competing to fill the last few empty tankers…