tests: fix broken source tests.

Fix various tests broken by source files changing or being deleted.

app/models/dmail.rb

@@ -155,7 +155,7 @@ class Dmail < ApplicationRecord
   end
 
   def validate_sender_is_not_limited
-    return if from.is_gold?
+    return if from.blank? || from.is_gold?
 
     if from.dmails.where("created_at > ?", 1.hour.ago).group(:to).reorder(nil).count.size >= 10
       errors[:base] << "You can't send dmails to more than 10 users per hour"