Update EndlessAdapter.java

Hello, Mark, I know that project is retired, but this changes can be helpful. I suggest sucj changes because it gives us opportunity to show error message. For example, we can retry network request. 
    @Override
    protected boolean onException(final View pendingView, final Exception e) {
        final View errorView = pendingView.findViewById(R.id.pending_error);
        errorView.setVisibility(View.VISIBLE);
        errorView.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(final View view) {
                onDataReady();
            }
        });

        final View progressView = pendingView.findViewById(R.id.pending_progress);
        progressView.setVisibility(View.GONE);

        return true;
    }