After you "check" multiple tables, "check again" is broken

I just committed #343908: Fatal error when the user click to the check since what was there previously was totally broken PHP errors. However, in testing, I noticed a related problem with the new code. If you select a few tables at admin/build/database and then press the "Check" button, you land on a page that shows the results of that check, with options to change the "Check type" and a "Check again" button. However, if you press the "Check again", it fails since the form thinks there are no tables selected.