[Net] Better EOF handling in HTTPRequest.

This fix request_completed being emitted two times, the first with the
result, the second as a failure when retrieving responses served with
read-until-EOF.

(cherry picked from commit d61cd469f1)

scene/main/http_request.cpp

@@ -376,6 +376,7 @@ bool HTTPRequest::_update_connection() {
 			} else if (client->get_status() == HTTPClient::STATUS_DISCONNECTED) {
 				// We read till EOF, with no errors. Request is done.
 				call_deferred("_request_done", RESULT_SUCCESS, response_code, response_headers, body);
+				return true;
 			}
 
 			return false;