修复滚动折叠导航栏在scroll-view下拉时出现闪烁背景的问题

pages/template/scroll-fold-nav/scroll-fold-nav.uvue

@@ -24,7 +24,7 @@
     },
     methods: {
       onScroll(e : ScrollEvent) {
-        (this.$refs['header'] as ComponentPublicInstance).$data['scrollTop'] = e.detail.scrollTop
+        (this.$refs['header'] as ComponentPublicInstance).$data['scrollTop'] = (e.detail.scrollTop<0?0:e.detail.scrollTop)
       },
       back() {
         // uni.navigateBack()  // 这么写用不了