fix: try catch runtime function call error

[dead-horse]

expect(function () {
      var tpl = '{{obj.error}}\n{{obj.error()}}';
      new XTemplate(tpl).render({
        obj: {
          error: error
        }
      });
    }).to.throwException(function (e) {
    expect(e.message).to.match(/Execute function `obj.error` Error: mock error/);
    expect(e.message).to.match(/line 2/);
  });

[yiminghe]

没测试用例...

[dead-horse]

@yiminghe 加上了

[dead-horse]

ping @yiminghe