Check if weekly workouts is zero before calculating duratio by week to avoid division by zero error

app.py

@@ -316,6 +316,7 @@ def render_users_and_workouts():
 
             # Calculate the workout counts and duration for the current week
             workout_counts_by_week.append(len(weekly_workouts))
+            if weekly_workouts:
                 duration_by_week.append(
                     int(sum([int(w['duration_minutes']) for w in weekly_workouts]))/len(weekly_workouts))