table 的嵌套子表格出现空白行

[DinoRun]

• I have searched the issues of this repository and believe that this is not a duplicate.

Version

1.3.10

Environment

vue2.5 Chrome75

Reproduction link

Steps to reproduce

在使用嵌套子表格的时候出现；

What is expected?

在没有子级数据的时候，希望不要出现 号及空白行；

What is actually happening?

在data数据没有child这个子级数据的时候，出现 号；点击加号出现了空白行；

[github-actions]

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