fix(证书资格审批): 处理有效期时间为空时的显示问题

src/views/bpm/handleTask/components/certificateQualifications/certificateQualificationsDialog.vue

@@ -20,7 +20,7 @@
       </el-descriptions-item>
       <el-descriptions-item :span="2">
         <template slot="label"> 有效期至 </template>
-        {{ form.validityStartTime + ' — ' + form.validityEndTime }}
+        {{ (form.validityStartTime ? form.validityStartTime : '') + ' — ' + (form.validityEndTime ? form.validityEndTime : '') }}
       </el-descriptions-item>
       <el-descriptions-item >
         <template slot="label"> 等级 </template>