Bug with deleting leading new lines in the block

[Zaczero]

When you put some extra new lines with Shift+Enter at the very beginning of the block and then try deleting it with Backspace the cursor jumps to the previous block.

[neSpecc]

Thanks, we will fix this in next releases.

[hampusborgos]

Notice the same issue, the following data will trigger the error:

{
    "time": 1557230398668,
    "blocks": [
        {
            "type": "header",
            "data": {
                "text": "A heading!",
                "level": 2
            }
        },
        {
            "type": "paragraph",
            "data": {
                "text": "<br>You can't delete the newline above this..."
            }
        }
    ],
    "version": "2.13.0"
}

[gohabereg]

Resolved by #826