Uncaught Error: Replacing non-existent child

Steps to reproduce: Click on the Divide pane vertically icon

**Atom**: 1.19.2 ia32
**Electron**: 1.6.9
**OS**: Microsoft Windows 10 Pro
**Thrown From**: [tool-bar](https://github.com/suda/tool-bar) package 1.1.0

### Stack Trace

Uncaught Error: Replacing non-existent child

```
At C:\Users\Charles\AppData\Local\atom\app-1.19.2\resources\app\src\pane-container.js:145

Error: Replacing non-existent child
at PaneContainer.replaceChild (~/AppData/Local/atom/app-1.19.2/resources/app/src/pane-container.js:145:47)
at Pane.module.exports.Pane.split (~/AppData/Local/atom/app-1.19.2/resources/app/src/pane.js:984:27)
at Pane.module.exports.Pane.splitRight (~/AppData/Local/atom/app-1.19.2/resources/app/src/pane.js:964:25)
at HTMLElement.pane:split-right (~/AppData/Local/atom/app-1.19.2/resources/app/src/register-default-commands.js:255:38)
at CommandRegistry.module.exports.CommandRegistry.handleCommandEvent (~/AppData/Local/atom/app-1.19.2/resources/app/src/command-registry.js:265:35)
at CommandRegistry.handleCommandEvent (~/AppData/Local/atom/app-1.19.2/resources/app/src/command-registry.js:3:65)
at CommandRegistry.module.exports.CommandRegistry.dispatch (~/AppData/Local/atom/app-1.19.2/resources/app/src/command-registry.js:166:25)
at executeCallback (/packages/tool-bar/lib/tool-bar-button-view.js:106:19)
at ToolBarButtonView._onClick (/packages/tool-bar/lib/tool-bar-button-view.js:70:7)
```

### Commands

```
-0:21.7.0 application:reopen-project (atom-pane.pane.active)
-0:12.2.0 pane:split-right (input.hidden-input)
```

### Non-Core Packages

```
atom-beautify 0.30.5
atom-handlebars 1.3.0
atom-shortcuts 0.0.2
atom-ternjs 0.18.3
auto-indent 0.5.0
autocomplete-modules 1.6.10
choose-pane 0.7.0
color-picker 2.2.5
cursor-history 0.12.0
firewatch-syntax 1.1.1
fonts 3.0.2
fox-syntax-theme 1.2.0
git-plus 7.9.3
highlight-selected 0.13.1
javascript-snippets 1.2.1
jquery-snippets 11.0.0
language-babel 2.71.0
language-cfml 0.17.1
language-javascript-jsx 0.3.7
language-sql-mysql 0.3.1
minimap 4.29.6
minimap-highlight-selected 4.6.1
minimap-pigments 0.2.2
minimap-selection 4.5.0
narrow 0.50.5
nord-atom-syntax 0.9.1
nord-atom-ui 0.11.0
open-this 0.4.0
paner 1.0.0
pigments 0.40.2
qolor 0.4.2
seti-syntax 1.1.3
seti-ui 1.9.0
tool-bar 1.1.0
tool-bar-atom 1.7.0
vim-mode-plus 0.97.2
```

Reproduce the failure by clicking the Divide pane vertically icon, then inspect lib/tool-bar-button-view.js at _onClick and executeCallback alongside the Atom pane.js and pane-container.js stack locations. Done means the command completes without the “Replacing non-existent child” error and vertical splitting still works.

Written by the indexing model from the issue text.