Window has incorrect size when using HiDPI scaling

Guake version:

```
Guake Terminal: 3.6.1
VTE: 0.56.1
VTE runtime: 0.56.1
Gtk: 3.24.8
```

Steps to reproduce:

- Use GNOME 3.32 with Wayland.
- Go to Settings -> Devices -> Monitors and set "Scale" to "200%".
- Start Guake

Expected results:

The Guake window shows up at the top of the screen, along the entire width of the screen.


Actual results:

The Guake window shows up at the top of the screen with unusual dimensions.


System information:

```
System:
Host: thinkpad-a285 Kernel: 5.0.11-300.fc30.x86_64 x86_64 bits: 64
Desktop: Gnome 3.32.1 Distro: Fedora release 30 (Thirty)
Machine:
Type: Laptop System: LENOVO product: 20MWCTO1WW v: ThinkPad A285
serial:
Mobo: LENOVO model: 20MWCTO1WW v: SDK0J40709 WIN serial:
UEFI: LENOVO v: R0XET33W (1.10 ) date: 11/07/2018
Battery:
ID-1: BAT0 charge: 34.0 Wh condition: 47.9/47.9 Wh (100%)
CPU:
Quad Core: AMD Ryzen 5 PRO 2500U w/ Radeon Vega Mobile Gfx type: MT MCP
speed: 1568 MHz max: 1600 MHz
Graphics:
Device-1: AMD Raven Ridge [Radeon Vega Series / Radeon Vega Mobile Series]
driver: amdgpu v: kernel
Display: wayland server: Fedora Project X.org 1.20.4 driver: amdgpu
resolution: 1536x864~60Hz
OpenGL: renderer: AMD RAVEN (DRM 3.27.0 5.0.11-300.fc30.x86_64 LLVM 8.0.0)
v: 4.5 Mesa 19.0.3
Network:
Device-1: Realtek RTL8822BE 802.11a/b/g/n/ac WiFi adapter driver: r8822be
Device-2: Realtek RTL8111/8168/8411 PCI Express Gigabit Ethernet
driver: r8169
Drives:
Local Storage: total: 238.47 GiB used: 78.89 GiB (33.1%)
Info:
Processes: 334 Uptime: 4h 55m Memory: 14.62 GiB used: 7.40 GiB (50.6%)
Shell: xonsh inxi: 3.0.32
```