wait for a downloader done/failed event before breaking the miner update loop

miner/miner.go

@@ -62,12 +62,13 @@ func (self *Miner) update() {
 			if shouldStart {
 				self.Start(self.coinbase, self.threads)
 			}
-		}
+
             // unsubscribe. we're only interested in this event once
             events.Unsubscribe()
             // stop immediately and ignore all further pending events
             break
 		}
+	}
 }
 
 func (m *Miner) SetGasPrice(price *big.Int) {