Reset as soon as possible.

src/convenient.rs

@@ -24,11 +24,15 @@ impl<'conn> Statement<'conn> {
     /// and `false` if the SQL returns an empty set.
     pub fn exists(&mut self, params: &[&ToSql]) -> Result<bool> {
         self.reset_if_needed();
+        let exists = {
             let mut rows = try!(self.query(params));
             match rows.next() {
                 Some(_) => Ok(true),
                 None => Ok(false),
             }
+        };
+        self.reset_if_needed();
+        return exists;
     }
 }