start_wifi(): ESP32 did not respond with a startup message

[dhalbert]

ESP32.reset() wrongly assumes that the ._uart exists when it checks for a startup message. But that's only true if you did .start_bluetooth(). If you just do .start_wifi(), ._uart won't be created and the check for the startup message will fail.

So .reset() should not check for a startup message if ._uart is None. You might wonder whether the code should always create a UART, but there are AirLift boards where the UART pins are not connected by default: you have to solder some jumpers.