FIX: Various fixes to support posts with no user (#8877)

* Do not grant badges for posts with no user
* Ensure instructions are correct in Change Owner modal
* Hide user-dependent actions from posts with no user
* Make PostRevisor work with posts with no user
* Ensure posts with no user can be deleted
* discourse-narrative-bot should ignore posts with no user
* Skip TopicLink creation for posts with no user

lib/cooked_post_processor.rb

@@ -56,7 +56,7 @@ class CookedPostProcessor
   end
 
   def grant_badges
-    return unless Guardian.new.can_see?(@post)
+    return if @post.user.blank? || !Guardian.new.can_see?(@post)
 
     BadgeGranter.grant(Badge.find(Badge::FirstEmoji), @post.user, post_id: @post.id) if has_emoji?
     BadgeGranter.grant(Badge.find(Badge::FirstOnebox), @post.user, post_id: @post.id) if @has_oneboxes

lib/guardian/post_guardian.rb

@@ -30,7 +30,7 @@ module PostGuardian
     return false unless (can_see_post.nil? && can_see_post?(post)) || can_see_post
 
     # no warnings except for staff
-    return false if (action_key == :notify_user && !is_staff? && opts[:is_warning].present? && opts[:is_warning] == 'true')
+    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]
@@ -71,7 +71,7 @@ module PostGuardian
       not(post.trashed?) &&
 
       # don't like your own stuff
-      not(action_key == :like && is_my_own?(post))
+      not(action_key == :like && (post.user.blank? || is_my_own?(post)))
     end
 
     !!result

lib/post_destroyer.rb

@@ -276,6 +276,8 @@ class PostDestroyer
   end
 
   def notify_deletion(reviewable)
+    return if @post.user.blank?
+
     allowed_user = @user.human? && @user.staff?
     return unless allowed_user && rs = reviewable.reviewable_scores.order('created_at DESC').first
 

lib/post_revisor.rb

@@ -180,13 +180,13 @@ class PostRevisor
       @fields.has_key?('raw') &&
       @editor.staff? &&
       @editor != Discourse.system_user &&
-      !@post.user.staff?
+      !@post.user&.staff?
     )
       PostLocker.new(@post, @editor).lock
     end
 
     # We log staff edits to posts
-    if @editor.staff? && @editor.id != @post.user.id && @fields.has_key?('raw') && !@opts[:skip_staff_log]
+    if @editor.staff? && @editor.id != @post.user_id && @fields.has_key?('raw') && !@opts[:skip_staff_log]
       StaffActionLogger.new(@editor).log_post_edit(
         @post,
         old_raw: old_raw