micropeak: Keep reading until we get valid data

micropeak: Keep reading until we get valid data

Don't stop just because we saw something invalid on the serial line;
let the user try again, or cancel when they get bored.

However, if the serial line disappears or some other fatal error
occurs, then do stop and put up an error dialog.

Signed-off-by: Keith Packard <keithp@keithp.com>