fix(接口定义): 修复接口定义请求参数请求头不显示的缺陷

--bug=1015884 --user=王孝刚 【接口测试】接口定义，接口用例中，有请求头时，不显示请求头数量统计，需要点到请求头tab才显示
https://www.tapd.cn/55049933/s/1226838

frontend/src/business/components/api/definition/components/request/http/ApiHttpRequestForm.vue

@@ -388,6 +388,9 @@ export default {
       if (!this.request.arguments) {
         this.request.arguments = [];
       }
+      if (this.headers && this.headers.length === 0) {
+        this.headers.push(new KeyValue({enable: true, name: '', value: ''}));
+      }
       if (this.request.hashTree) {
         this.initStepSize(this.request.hashTree);
         this.historicalDataProcessing(this.request.hashTree);