[Bug] horizontal term's size goes wrong after a special exit pattern

[qvieth]

https://user-images.githubusercontent.com/71810726/127414090-4d99a486-51ab-4f65-9af4-13a47cb44e97.mp4

Steps to reproduce :

1. open horizontal term
2. change to non-terminal buffer
3. :q
4. open horizontal term
5. use exit command
6. open horizontal term <-- bug happens

Setting persist_size = false seems to fix the problem(but idk why).