fixed defects found by coverity scan

I don't think this was the intention. if you look at 1a5fcd7, you'll see the `descriptor` field had values from the enum `KAZE::DESCRIPTOR_TYPE`. However, in 029a8c4, the enum was removed, as well as all usage of the `descriptor` field. I'm guessing that the author simply forgot to remove the field, and that is what you should do. (I'm assuming that Coverity complains that the field is unused.)