Fix #0017605: Regression issue with upgrade step 184

Background and comments / rational on this commit are in http://www.mantisbt.org/bugs/view.php?id=17605.
Two problems with that: 

a) in current installer, I'm not sure we support that - i'll check though, as it might be worth adding for obvious reasons

b) In this particular case, in theory this can never be hit - to hit this, you'd need to have invalid data stored in your database that wasn't generated by Mantis, so i'm not necessarily sure we can add 'useful information' - I for one would want to see a copy of the filters table if someone hit this case.