Fixed #25610 -- Reverted removal of request.current_app in {% url %} tag.

The deprecation removal in 5e450c52aa
removed too much.

django/template/defaulttags.py

@@ -434,9 +434,12 @@ class URLNode(Node):
         }
         view_name = self.view_name.resolve(context)
         try:
-            current_app = context.request.resolver_match.namespace
+            current_app = context.request.current_app
         except AttributeError:
-            current_app = None
+            try:
+                current_app = context.request.resolver_match.namespace
+            except AttributeError:
+                current_app = None
         # Try to look up the URL. If it fails, raise NoReverseMatch unless the
         # {% url ... as var %} construct is used, in which case return nothing.
         url = ''