FIX: Sending a PM through a flag on a deleted post

Because we allow all the other flag types on a deleted post we should be
able to send a pm to the user letting them know why we deleted their
post.

Bug report:

https://meta.discourse.org/t/-/161156

lib/guardian/post_guardian.rb

@@ -33,7 +33,7 @@ module PostGuardian
     return false if action_key == :notify_user && (post.user.blank? || (!is_staff? && opts[:is_warning].present? && opts[:is_warning] == 'true'))
 
     taken = opts[:taken_actions].try(:keys).to_a
-    is_flag = PostActionType.notify_flag_types[action_key]
+    is_flag = PostActionType.notify_flag_types[action_key] || PostActionType.custom_types[action_key]
     already_taken_this_action = taken.any? && taken.include?(PostActionType.types[action_key])
     already_did_flagging      = taken.any? && (taken & PostActionType.notify_flag_types.values).any?
 

spec/components/guardian_spec.rb

@@ -112,6 +112,8 @@ describe Guardian do
     it "returns false when the post is deleted" do
       post.deleted_at = Time.now
       expect(Guardian.new(user).post_can_act?(post, :like)).to be_falsey
+      expect(Guardian.new(admin).post_can_act?(post, :spam)).to be_truthy
+      expect(Guardian.new(admin).post_can_act?(post, :notify_user)).to be_truthy
     end
 
     it "works as expected for silenced users" do