Remove code that breaks rendering of forms for models with an array field

Cleaned up this nasty bit which completely breaks form screen for models with an array field in the latest version of formage: 

    TypeError: Cannot call method 'render' of undefined
        at render_field (C:\projects\<project>\node_modules\formage-admin\forms\fields.js:521:23)
        at render_fields (C:\projects\<project>\node_modules\formage-admin\forms\fields.js:508:21)
        at Class.exports.ListField.BaseField.extend.render_list_item (C:\projects\<project>\node_modules\formage-admin\forms\fields.js:542:13)
        at render_template (C:\projects\<project>\node_modules\formage-admin\forms\fields.js:461:18)
        at Class.exports.ListWidget.Widget.extend.render (C:\projects\<project>\node_modules\formage-admin\forms\widgets.js:315:9)
        at Class.exports.ListField.BaseField.extend.render (C:\projects\<project>\node_modules\formage-admin\forms\fields.js:471:21)
        at Class.exports.BaseField.Class.extend.render_with_label (C:\projects\<project>\node_modules\formage-admin\forms\fields.js:91:14)
        at render_fields (C:\projects\<project>\node_modules\formage-admin\forms\forms.js:210:49)
        at Class.exports.BaseForm.Class.extend.render (C:\projects\<project>\node_modules\formage-admin\forms\forms.js:239:13)
        at C:\projects\<project>\node_modules\formage-admin\forms\forms.js:250:18