fix: 添加活动为空时的硬币收集提示

@@ -121,6 +121,12 @@ const handleGeneratePoster = (item) => {
 }
 
 const handleCollectCoins = async () => {
+  if (activities.value.length === 0) {
+    showToast({
+      message: '暂无活动可收集',
+    })
+    return
+  }
   // 从缓存获取用户信息
   const cachedUserInfo = localStorage.getItem('cached_user_info')
   if (cachedUserInfo) {