Fix(云灵AI):[#5395]输入框文本超字符限制无提示，超限新增内容输入框不显示，发送后又显示-2

aiChat/mixins/chatMixinsV2.js

@@ -217,6 +217,14 @@ export const chatMixinsV2 = {
         handleLoginFailure()
         return
       }
+      if (params.prompt.length > 500) {
+        uni.showToast({
+          title: "字数已超出限制",
+          icon: "none",
+          duration: 5000
+        })
+        return
+      }
       if (this.loading) return
       const prompt = params.prompt.substr(0, 500)
       if (params.init !== 1) {