Ensure Issuable respond to :total_time_spent before calling it

Signed-off-by: Rémy Coutable <remy@rymai.me>

app/models/concerns/issuable.rb

@@ -280,7 +280,7 @@ module Issuable
       end
     end
 
-    if old_total_time_spent != total_time_spent
+    if self.respond_to?(:total_time_spent) && old_total_time_spent != total_time_spent
       changes[:total_time_spent] = [old_total_time_spent, total_time_spent]
     end
 

app/services/issuable_base_service.rb

@@ -174,7 +174,7 @@ class IssuableBaseService < BaseService
     old_labels = issuable.labels.to_a
     old_mentioned_users = issuable.mentioned_users.to_a
     old_assignees = issuable.assignees.to_a
-    old_total_time_spent = issuable.total_time_spent
+    old_total_time_spent = issuable.total_time_spent if issuable.respond_to?(:total_time_spent)
 
     label_ids = process_label_ids(params, existing_label_ids: issuable.label_ids)
     params[:label_ids] = label_ids if labels_changing?(issuable.label_ids, label_ids)