Fix Echo.Serve() will no serve on HTTP port correctly when there is a…

…lready TLSListener set to Echo instance. (labstack#1785)

This is problem when user tries to use HTTP (e.Listener) and HTTPS (e.TLSListener) with same Echo instance.

echo.go

@@ -660,7 +660,7 @@ func (e *Echo) Start(address string) error {
 		return err
 	}
 	e.startupMutex.Unlock()
-	return e.serve()
+	return e.Server.Serve(e.Listener)
 }
 
 // StartTLS starts an HTTPS server.
@@ -740,8 +740,12 @@ func (e *Echo) StartServer(s *http.Server) (err error) {
 		e.startupMutex.Unlock()
 		return err
 	}
+	if s.TLSConfig != nil {
+		e.startupMutex.Unlock()
+		return s.Serve(e.TLSListener)
+	}
 	e.startupMutex.Unlock()
-	return e.serve()
+	return s.Serve(e.Listener)
 }
 
 func (e *Echo) configureServer(s *http.Server) (err error) {
@@ -782,13 +786,6 @@ func (e *Echo) configureServer(s *http.Server) (err error) {
 	return nil
 }
 
-func (e *Echo) serve() error {
-	if e.TLSListener != nil {
-		return e.Server.Serve(e.TLSListener)
-	}
-	return e.Server.Serve(e.Listener)
-}
-
 // ListenerAddr returns net.Addr for Listener
 func (e *Echo) ListenerAddr() net.Addr {
 	e.startupMutex.RLock()