HTTPRequest: Improve response when disconnecting while downloading

Previously if a disconnect occured while downloading a non recoverable error was displayed. This PR attempts to fix this by making sure `request_completed` signal is emitted with an `STATUS_CONNECTION_ERROR` response code.

(cherry picked from commit 70c39737db)

scene/main/http_request.cpp

@@ -347,6 +347,9 @@ bool HTTPRequest::_update_connection() {
 			}
 
 			client->poll();
+			if (client->get_status() != HTTPClient::STATUS_BODY) {
+				return false;
+			}
 
 			PoolByteArray chunk = client->read_response_body_chunk();
 			downloaded.add(chunk.size());