修复音频作答bug

src/modules/oe/views/examPaperDetail.vue

@@ -59,7 +59,7 @@
                 <span v-html="questionUnit.correctAnswer"></span>
               </div>
               <div
-                v-if="questionUnit.answerType!=='SINGLE_AUDIO'"
+                v-if="questionUnit.answerType!=='SINGLE_AUDIO' || (questionUnit.answerType==='SINGLE_AUDIO' && (questionUnit.studentAnswer==null || questionUnit.studentAnswer==''))"
                 style="color: blue;font-weight: bold;"
               >
                 学生答案: