[android] onloadmore of scroller is not executed when loadmoreoffset is not set

[ghost]

Brief Description of the PR

On the web and iOS, do not set "loadmoreoffset" can trigger the loadmore event, but not on Android.
This pr solved it.

Checklist

• Demo

[ghost]

I have a same pr, but Maven read timed out in CI build.
Now I want to rebase the newest commit, but the repo have too many changes and I have too many conflicts.So I just delete my repo, fork the repo and pull the request again.

[weex-bot]

	Warnings
⚠️	Current pr not bind the milestone
⚠️	If you update the code, maybe you should update the documentation and add the documentation link in the PR description. here is the guide about how to contribute documentation: https://github.com/apache/incubator-weex/blob/master/CONTRIBUTING.md#contribute-code-or-document

	Messages
📖	danger test finished.

Generated by 🚫 dangerJS against 9c2a66e

[YorkShen]

Please rebase to master branch, as there is a conflict.