Bug 1020766 - fix [Flatfish][Gallery]Gallery app shows last-deleted photo in  the preview window

https://bugzilla.mozilla.org/show_bug.cgi?id=1020766
I'm generally in favor of verbose comments, but this comment explains a bug rather than explaining what the function is doing, so I'd suggest you just leave it out.  Or clean it up so it has proper punctuation, etc.