farm mode activation and farm number initialization handled when upgrading firmware versions and when flashing to new eeprom

Firmware/Marlin_main.cpp

@@ -1130,7 +1130,8 @@ void setup()
 #endif
   farm_mode = eeprom_read_byte((uint8_t*)EEPROM_FARM_MODE);
   EEPROM_read_B(EEPROM_FARM_NUMBER, &farm_no);
-  if (farm_mode == 0xFF && farm_no == 0) farm_mode = false; //if farm_mode has not been stored to eeprom yet and farm number is set to zero, deactivate farm mode
+  if ((farm_mode == 0xFF && farm_no == 0) || (farm_no == 0xFFFF)) farm_mode = false; //if farm_mode has not been stored to eeprom yet and farm number is set to zero or EEPROM is fresh, deactivate farm mode 
+  if (farm_no == 0xFFFF) farm_no = 0;
   if (farm_mode)
   {
 	  prusa_statistics(8);