Pack & Go - pre-warning of inaccessible drive

[DigPeter]

When 'packing', I omitted to connect the external drive to which it should be saved.  Pack & Go went through the diagnosis before a dialog announced failure.  The protocol stated that this was a failure to write the file. Not really understanding why this should be, I did this a second time with the same result, before realising my mistake.  Could Pack & Go please test first that the drive/folder is accessible and if not, give a warning to this effect.  This could save ordinary punters like myself some angst!

[Mario]

Done for 156.