fix(merch/detail): 修复头部高度重复初始化的问题

添加headerHeightInited标记，避免merch数据更新时重复调用初始化方法

pages_promotion/merch/detail.vue

@@ -321,16 +321,19 @@ export default {
 	data() {
 		return {
 			headerHeight: 320,
-			screenWidth: uni.getSystemInfoSync().windowWidth
+			screenWidth: uni.getSystemInfoSync().windowWidth,
+			headerHeightInited: false
 		};
 	},
 	mixins: [list],
 	watch: {
 		merch: {
 			handler() {
-				this.$nextTick(() => {
+				if (!this.headerHeightInited) {
-					this.initHeaderHeight();
+					this.$nextTick(() => {
-				});
+						this.initHeaderHeight();
+					});
+				}
 			},
 			deep: true
 		}
@@ -349,8 +352,9 @@ export default {
 			setTimeout(() => {
 				const query = uni.createSelectorQuery().in(this);
 				query.select('.head-wrap').boundingClientRect(rect => {
-					if (rect) {
+					if (rect && rect.height > 0) {
 						this.headerHeight = (rect.height / this.screenWidth) * 750;
+						this.headerHeightInited = true;
 					}
 				}).exec();
 			}, 100);