fix(测试用例): 用例模板中带有多选下拉框自定义字段时导入报错

--bug=1007126 --user=lyh 【github#6699】用例模板中带有多选下拉框自定义字段时导入报错
https://www.tapd.cn/55049933/s/1059014

frontend/src/common/js/custom_field.js

@@ -58,6 +58,11 @@ export function parseCustomField(data, template, customFieldForm, rules, oldFiel
       for (let i = 0; i < data.customFields.length; i++) {
         let customField = data.customFields[i];
         if (customField.name === item.name) {
+          if (customField.type === 'multipleSelect') {
+            if (typeof (customField.value) === 'string' || customField.value instanceof String) {
+              customField.value = JSON.parse(customField.value);
+            }
+          }
           setDefaultValue(item, customField.value);
           break;
         }

frontend/src/common/js/tableUtils.js

@@ -469,7 +469,12 @@ export function getCustomFieldValue(row, field, members) {
         else if (['multipleSelect', 'checkbox'].indexOf(field.type) > -1) {
           if (item.value) {
             let values = '';
-            if (item.value instanceof Array) {
+            try {
+              if (field.type === 'multipleSelect') {
+                if (typeof (item.value) === 'string' || item.value instanceof String) {
+                  item.value = JSON.parse(item.value);
+                }
+              }
               item.value.forEach(v => {
                 for (let j = 0; j < field.options.length; j++) {
                   let option = field.options[j];
@@ -480,6 +485,8 @@ export function getCustomFieldValue(row, field, members) {
                   }
                 }
               });
+            } catch (e) {
+              values = '';
             }
             return values;
           }