Fix the bug that enforcer with no adapter doesn't call BuildRoleLinks…

…(), fix: #247

enforcer.go

@@ -211,7 +211,7 @@ func (e *Enforcer) ClearPolicy() {
 // LoadPolicy reloads the policy from file/database.
 func (e *Enforcer) LoadPolicy() error {
 	e.model.ClearPolicy()
-	if err := e.adapter.LoadPolicy(e.model); err != nil {
+	if err := e.adapter.LoadPolicy(e.model); err != nil && err.Error() != "invalid file path, file path cannot be empty" {
 		return err
 	}
 
@@ -235,7 +235,7 @@ func (e *Enforcer) LoadFilteredPolicy(filter interface{}) error {
 	default:
 		return errors.New("filtered policies are not supported by this adapter")
 	}
-	if err := filteredAdapter.LoadFilteredPolicy(e.model, filter); err != nil {
+	if err := filteredAdapter.LoadFilteredPolicy(e.model, filter); err != nil && err.Error() != "invalid file path, file path cannot be empty" {
 		return err
 	}