fix no triggerEvent() function when invoke this.$emit() in page.

src/platforms/mp-alipay/runtime/wrapper/page-parser.js

@@ -17,6 +17,7 @@ import {
   handleRef,
   handleLink,
   initBehavior,
+  triggerEvent,
   initChildVues,
   initSpecialMethods
 } from './util'
@@ -85,7 +86,8 @@ export default function parsePage (vuePageOptions) {
     },
     __r: handleRef,
     __e: handleEvent,
-    __l: handleLink
+    __l: handleLink,
+    triggerEvent
   }
 
   initHooks(pageOptions, hooks, vuePageOptions)

src/platforms/mp-alipay/runtime/wrapper/util.js

@@ -122,7 +122,7 @@ export function handleRef (ref) {
 }
 
 export function triggerEvent (type, detail, options) {
-  const handler = this.props[customize('on-' + type)]
+  const handler = this.props && this.props[customize('on-' + type)]
   if (!handler) {
     return
   }