message: GO: Minor tweak to long-running operations.
  If error is nil don't write it to error channel just close it.
diff: @@ -70,8 +70,10 @@ func (client @(Model.Owner)) @(Model.MethodSignature) (@Model.MethodReturnSignat
  @:var result @(Model.MethodReturnType)
  @:defer func() {
  - @:resultChan <- result
  + @:if err != nil {
  @:errChan <- err
  + @:}
  + @:resultChan <- result
  @:close(resultChan)
  @:close(errChan)
  @:}()
  