Ato Araki

Fixed a problem with the drawPngUrl function. `while (http.connected())` causes an infinite loop. I used this [example](https://github.com/espressif/arduino-esp32/blob/7856de7a57420e494176c16c5138174fe2c1dad0/libraries/HTTPClient/examples/StreamHttpClient/StreamHttpClient.ino#L59-L85) as a reference.

Hi akio-san, I find panic on the SearchParam type assertion. ```go package example_test import ( "testing" "ros" ) func TestSearchParam(t *testing.T) { node := ros.NewNode("/example_node") _, err := node.SearchParam("not_found") if...