Maintenance: Applied Zammad/PreferNegatedIfOverUnless on custom cops.

.rubocop/cop/zammad/exists_condition.rb

@@ -65,7 +65,7 @@ module RuboCop
         end
 
         def check_node(node)
-          return unless node
+          return if !node
 
           if keyword_bang?(node)
             receiver, = *node

.rubocop/cop/zammad/prefer_negated_if_over_unless.rb

@@ -20,7 +20,7 @@ module RuboCop
               'negative conditions.'.freeze
 
         def on_if(node)
-          return unless node.unless?
+          return if !node.unless?
 
           add_offense(node, message: MSG)
         end