NERDTree resize conflict

Thanks for this amazing project!

#### Issue description

If a NERDTree window is open, the windows are not resized back to their correct sizes.

#### Steps to reproduce

Split your editor horizontally and vertically a few times and open NERDTree. Do a CtrlSF search and close the window again. The previous editor splits do not get their old sizes back.

#### Things about your system and environment（请在此填写你的系统信息）

| field | value |
|:-------:|:------------------------------------:|
| os | Linux Debian testing |
| vim | (g)vim 7.8 including patches 1-716 |
| backend | ag 2.2.0 |
| locale | en_US.UTF-8 |

```vim
let g:ctrlsf_position = 'bottom'
```

**Let me now if you can't reproduce this easily, and I will provide more information.**