Buffer overrun in encode_6_and_2()

[TomCh]

This code overruns at location==1:

	while(location) {
		--location;
		dest[location] ^= dest[location-1];
	}

So should be:

	while(location>1) {
		--location;
		dest[location] ^= dest[location-1];
	}

I built with VS2017 (and VS2008) and it creates broken .woz images, as the 1st nibble of each sector is wrong.

[Thomas Harte]

Thanks, sorry for not noticing this earlier. You're completely right, corrected.