You shouldn't worry about the bot.  The bug is apparently only for images with unusual characters, such as accents.  You can just avoid them for now.  Or just delete the message from your talk page and mark the faulty page for speedy deletion (this criterion seems to fit).  I believe you can also request white-listing at the  talk page, though I wouldn't bother.  One other thing is that if it notices that there is no rationale, it will inform you because you were the last one to upload a new version.  What I have done so far is to just copy the warning over to the talk page of the original uploader, if it looks like they are still active.  Otherwise I just add whatever seems appropriate.  I (generally) won't rescale an image I feel has no place, so most times I don't have a big problem with adding rationales.  But as I said, if the original uploader is present, it is their problem.  As for what should be in a rationale, well, it should generally point out how these criteria are met.  If the standard  template is filled out, you're generally well-covered.  I've started writing up the most common stuff I encounter .  Also, feel free to dig through my contributions and look for edits with the summary "Fair use rationale added" for further inspiration.