Actually, no, there isn't. Rather annoying when you're trying to do housekeeping.
I cheat and use a spreadsheet. First, nab a list of all the projects from Admin -> Projects. Second, create a saved filter for "all issues". Third, whack the filter into a dashboard gadget of "Filter statistics" and choose "project". The gadget now lists every project that has at least one issue. Take that list into your spreadsheet and subtract it from the full list. (As a minor bonus, the gadget will also be telling you if you've got projects with only a handful of issues, which are also candidates for merge/delete)
I wrote a housekeeping report which does this properly. Sadly, I've never had time to consider publishing it!
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