Change field receipt handling to work properly with Minetest 0.4.8.

mesecons_microcontroller/init.lua

@@ -98,6 +98,9 @@ minetest.register_node(nodename, {
 		meta:set_string("eeprom", r)
 	end,
 	on_receive_fields = function(pos, formanme, fields, sender)
+		if fields.quit then
+			return
+		end
 		local meta = minetest.get_meta(pos)
 		if fields.band then
 			fields.code = "sbi(C, A&B) :A and B are inputs, C is output"