Try harder to restore original settings. Fixes #991

root cause is that settings are cached and after override
MENU_ITEMS is modified. In case of intermediary failures it was
not restored and other pages were showing bogus menu items.

This seems to resolve the problem although it's now very hard to
reproduce this problem reliably, hence no actual test.

tcms/core/response.py

@@ -1,7 +1,8 @@
-# Copyright (c) 2019 Alexander Todorov <atodorov@MrSenko.com>
+# Copyright (c) 2019-2020 Alexander Todorov <atodorov@MrSenko.com>
 
 # Licensed under the GPL 2.0: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 
+from django.conf import settings
 from django.template.response import TemplateResponse
 
 
@@ -33,5 +34,22 @@ def render_to_response(self, context, **response_kwargs):
     modify_settings = None
 
     def render(self):
-        with self.modify_settings:  # pylint: disable=not-context-manager
-            return super().render()
+        try:
+            with self.modify_settings:  # pylint: disable=not-context-manager
+                return super().render()
+        finally:
+            # if this attribute is still set that means disabling settings override
+            # failed which leads to navbar showing bogus menu items, see
+            # https://github.com/kiwitcms/Kiwi/issues/991
+            # => try to restore the original unmodified settings, see
+            # django.test.utils.override_settings().disable()
+            #
+            # NOTE: the only way to reproduce this reliably ATM is by raising exception
+            # in .disable() before restoring the original settings although I can see
+            # the problem on tcms.kiwitcms.org after the last restart 1 week ago!
+            # Maybe the switch to CBV and this response class made #991 harder to
+            # reproduce. It was easier to reproduce in the past by triggering some kind
+            # of exception in the FBV which used modify_settings() !!!
+            if hasattr(self.modify_settings, 'wrapped'):
+                settings._wrapped = self.modify_settings.wrapped  # pylint: disable=protected-access
+                del self.modify_settings.wrapped