compare: make sure to not do any redirects for XHR requests types.

This can lead to page-in-page rendering when using ajax compare loading.

rhodecode/apps/repository/views/repo_compare.py

@@ -68,8 +68,10 b' class RepoCompareView(RepoAppView):'
                 return repo.scm_instance().EMPTY_COMMIT
             h.flash(h.literal(_('There are no commits yet')),
                     category='warning')
-            raise HTTPFound(
-                h.route_path('repo_summary', repo_name=repo.repo_name))
+            if not partial:
+                raise HTTPFound(
+                    h.route_path('repo_summary', repo_name=repo.repo_name))
+            raise HTTPBadRequest()
 
         except RepositoryError as e:
             log.exception(safe_str(e))