guake --split-vertical in startup script doesn't place the window separator in the middle

I have a startup script for Guake and I use something like this:
```bash
guake -r "0"
guake -n ~ -r "1"
guake -n ~ -r "2"
guake --split-vertical
guake -n ~ -r "3"
guake -n ~ -r "4"
guake -s 0
````
Guake successfully creates the tabs and does the vertical split in tab 2--but the window separator is collapsed to the left, so only one of the two terminals is visible. I can move the window separator manually to the middle to see both terminals.

My expected behaviour is that the window separator is in the middle of the window to see both terminals without manually move the window separator.

I achieved this by modifying the startup script to this:
```bash
guake --show

guake -r "0"
guake -n ~ -r "1"
guake -n ~ -r "2"
guake --split-vertical
guake -n ~ -r "3"
guake -n ~ -r "4"
guake -s 0

guake --hide
````

But I don't want to have Guake visible during the startup. Is it possible to execute `guake --split-vertical` without having Guake visible?

-------------------------------------------------------------------------------

$ guake --support

Guake Version: 3.6.3

Vte Version: 0.52.2

Vte Runtime Version: 0.52.2

--------------------------------------------------
GTK+ Version: 3.22.30

GDK Backend: GdkX11.X11Display

--------------------------------------------------
Desktop Session: mate

--------------------------------------------------
Display: :0

RGBA visual: True

Composited: True

* Monitor: 0 - DP-1
* Geometry: 1920 x 1200 at 0, 0
* Size: 518 x 324 mm²
* Primary: True
* Refresh rate: 59.95 Hz
* Subpixel layout: unknown
* Monitor: 1 - DP-3
* Geometry: 1920 x 1200 at 3840, 0
* Size: 518 x 324 mm²
* Primary: False
* Refresh rate: 59.95 Hz
* Subpixel layout: unknown
* Monitor: 2 - DP-5
* Geometry: 1920 x 1200 at 1920, 0
* Size: 518 x 324 mm²
* Primary: False
* Refresh rate: 59.95 Hz
* Subpixel layout: unknown