HTTPClientWrapper: Initialize buffer variables. D'Oh.

src/http_client_wrapper.cpp

@@ -72,6 +72,9 @@ bool HTTPClientWrapper::_request(String method, String url, uint32_t offset, uin
 		DEBUG("Unexpected HTTP return code %d. Cancelling.\n", status);
 		return false;
 	}
+
+	_buffer_position = 0;
+	_buffer_length = 0;
 	
 	_connected = true;
 	_length = _http->getSize() + offset;