Fix Error in find_question_label.

common/lib/capa/capa/capa_problem.py

@@ -562,7 +562,12 @@ class LoncapaProblem(object):
         """
         _ = get_gettext(self.capa_system.i18n)
         # Some questions define a prompt with this format:   >>This is a prompt<<
-        prompt = self.problem_data[answer_id].get('label')
+        log_error = False
+        try:
+            prompt = self.problem_data[answer_id].get('label')
+        except KeyError:
+            log_error = True
+            prompt = self.problem_data.get(answer_id, {}).get('label')
 
         if prompt:
             question_text = prompt.striptags()
@@ -607,6 +612,11 @@ class LoncapaProblem(object):
                 question_nr = int(answer_id.split('_')[-2]) - 1
                 question_text = _("Question {0}").format(question_nr)
 
+        if log_error:
+            log.error(
+                'KeyError: answer_id: %s, Problem data: %s, question_text: %s',
+                (answer_id, self.problem_data, question_text)
+            )
         return question_text
 
     def find_answer_text(self, answer_id, current_answer):