flags: disallow flagging pending posts.

app/models/post_flag.rb

@@ -158,6 +158,7 @@ class PostFlag < ActiveRecord::Base
   end
 
   def validate_post
+    errors[:post] << "is pending and cannot be flagged" if post.is_pending? && !is_deletion
     errors[:post] << "is locked and cannot be flagged" if post.is_status_locked?
     errors[:post] << "is deleted" if post.is_deleted?
   end