Fix project deletion when feature visibility is set to private

Projects that are destroyed are put in the pending_delete state.
The ProjectDestroyWorker checks whether the current user has
access, but since the ProjectFeature class uses the default scope
of the Project, it will not be able to find the right project.

This was a regression in 8.12 that caused the following stack trace:

```
NoMethodError: undefined method `team' for nil:NilClass
  from app/models/project_feature.rb:62:in `get_permission'
  from app/models/project_feature.rb:34:in `feature_available?'
  from app/models/project.rb:21:in `feature_available?'
  from app/policies/project_policy.rb:170:in `disabled_features!'
  from app/policies/project_policy.rb:29:in `rules'
  from app/policies/base_policy.rb:82:in `block in abilities'
  from app/policies/base_policy.rb:113:in `collect_rules'
  from app/policies/base_policy.rb:82:in `abilities'
  from app/policies/base_policy.rb:50:in `abilities'
  from app/models/ability.rb:64:in `uncached_allowed'
  from app/models/ability.rb:58:in `allowed'
  from app/models/ability.rb:49:in `allowed?'
  from app/services/base_service.rb:11:in `can?'
  from lib/gitlab/metrics/instrumentation.rb:155:in `block in can?'
  from lib/gitlab/metrics/method_call.rb:23:in `measure'
  from lib/gitlab/metrics/instrumentation.rb:155:in `can?'
  from app/services/projects/destroy_service.rb:18:in `execute'
```

Closes #22948

1 files changed, 4 insertions, 1 deletions

diff --git a/app/models/project_feature.rb b/app/models/project_feature.rb
index 8c9534c3565..530f7d5a30e 100644
--- a/app/models/project_feature.rb
+++ b/app/models/project_feature.rb
@@ -20,7 +20,10 @@ class ProjectFeature < ActiveRecord::Base
 
   FEATURES = %i(issues merge_requests wiki snippets builds)
 
-  belongs_to :project
+  # Default scopes force us to unscope here since a service may need to check
+  # permissions for a project in pending_delete
+  # http://stackoverflow.com/questions/1540645/how-to-disable-default-scope-for-a-belongs-to
+  belongs_to :project, -> { unscope(where: :pending_delete) }
 
   default_value_for :builds_access_level,         value: ENABLED, allows_nil: false
   default_value_for :issues_access_level,         value: ENABLED, allows_nil: false