Renders an additional non active input field

If editor has no initial input data, then after pressing **enter** in an empty input field there is created an addition not intended input field which does nothing.

### How to reproduce:

1. Delete data object from **new EditorJS** in the example.html
2. In browser, press **tab** twice and then **enter** to create image input field
3. Press **enter** again

Result looks like this:
But pasting image url into the second field does nothing.

打开 example.html，并在浏览器中重现空编辑器的操作序列：按两次 Tab，按 Enter 创建图像输入，然后再次按 Enter。跟踪附加输入字段的处理，并验证按 Enter 不会创建无效字段；粘贴图像 URL 应继续在预期字段中正常工作。

由索引模型根据 Issue 内容生成。