account for edge case if student or teacher talk is zero

handler.py

@@ -144,8 +144,8 @@ class Transcript:
         teacher_percentage = round(
             (teacher_words / (teacher_words + student_words)) * 100)
         student_percentage = 100 - teacher_percentage
-        avg_teacher_length = teacher_words / teacher_utt_count
-        avg_student_length = student_words / student_utt_count
+        avg_teacher_length = teacher_words / teacher_utt_count if teacher_utt_count > 0 else 0
+        avg_student_length = student_words / student_utt_count if student_utt_count > 0 else 0
         return {'teacher': teacher_percentage, 'student': student_percentage}, {'teacher': avg_teacher_length, 'student': avg_student_length}
 
     def get_word_clouds(self):