changelog: let 'Open new pull request' use the currently topmost changeset

rhodecode/templates/changelog/changelog.html

@@ -194,7 +194,9 b''
                         else{
                             YUD.setStyle('rev_range_container','display','none');
                             YUD.setStyle('rev_range_clear','display','none');
-                            YUD.get('open_new_pr').href = pr_tmpl
+                            if (checkboxes){
+                                YUD.get('open_new_pr').href = pr_tmpl + '?rev_end={0}'.format(checkboxes[0].name);
+                            }
                             YUD.setStyle('compare_fork','display','');
                         }
                     };