fix(merch/detail): 防止重复初始化头部高度

1. 新增headerHeightInited状态避免重复调用initHeaderHeight
2. 在initHeaderHeight中增加商品名称校验防止无效执行
3. 仅在页面首次获取商品数据后初始化头部高度

pages_promotion/merch/detail.vue

@@ -322,7 +322,8 @@ export default {
 		return {
 			headerHeight: 320,
 			screenWidth: uni.getSystemInfoSync().windowWidth,
-			changeStyleDebounce: null
+			changeStyleDebounce: null,
+			headerHeightInited: false
 		};
 	},
 	mixins: [list],
@@ -337,7 +338,9 @@ export default {
 					if (res.code >= 0 && res.data) {
 						this.merch = res.data;
 						this.$nextTick(() => {
+							if (!this.headerHeightInited) {
 								this.initHeaderHeight();
+							}
 						});
 					}
 				}
@@ -353,10 +356,13 @@ export default {
 			}
 		},
 		initHeaderHeight() {
+			if (!this.merch || !this.merch.merch_name) return;
+			if (this.headerHeightInited) return;
 			const query = uni.createSelectorQuery().in(this);
 			query.select('.head-wrap').boundingClientRect(rect => {
 				if (rect && rect.height > 0) {
 					this.headerHeight = (rect.height / this.screenWidth) * 750;
+					this.headerHeightInited = true;
 				}
 			}).exec();
 		},