Fix nil pointer dereference when err is nil

pkg/drivers/donut/donut.go

@@ -48,9 +48,11 @@ func Start(path string) (chan<- string, <-chan error, drivers.Driver) {
 	// TODO donut driver should be passed in as Start param and driven by config
 	var err *iodine.Error
 	s.donut, err = donut.NewDonut(path)
-	err = err.Annotate(map[string]string{"path": path})
 	if err != nil {
-		log.Println(err.EmitHumanReadable())
+		err = err.Annotate(map[string]string{"path": path})
+		if err != nil {
+			log.Println(err.EmitHumanReadable())
+		}
 	}
 
 	go start(ctrlChannel, errorChannel, s)