Fix coins calculation

Author: nygrenh

app/controllers/api/v8/organizations/courses/exercises_controller.rb

@@ -96,7 +96,11 @@ def show
               completed_exercises_count = course.submissions.where(all_tests_passed: true, user: current_user).distinct.select(:exercise_name).count
               total_model_solution_tokens = completed_exercises_count / grant_model_solution_token_every_nth_completed_exercise + (course.initial_coin_stash || 0)
 
-              tokens_used = ModelSolutionTokenUsed.where(user: current_user, course: course).count
+              tokens_used = if course.large_exercises_consume_more_coins?
+                ModelSolutionTokenUsed.where(user: current_user, course: course).sum(:cost)
+              else
+                ModelSolutionTokenUsed.where(user: current_user, course: course).count
+              end
               available_model_solution_tokens = total_model_solution_tokens - tokens_used
             end