Windows desktop: Ctrl+- zooms out, but Ctrl++ does not zoom back in or reset

### Steps to reproduce
1. Open Element Desktop on Windows.
2. Press `Ctrl+-` to zoom out.
3. Try to zoom back in with `Ctrl++` (or `Ctrl+=`).
4. Look in Settings for a way to increase or reset the zoom level.
5. Close and reopen the app.

### Outcome
#### What did you expect?
`Ctrl++` should zoom back in again, or there should be an obvious setting to increase/reset the zoom level. After restarting the app, it should not remain stuck at the previously reduced zoom level without a way to restore it.

#### What happened instead?
`Ctrl+-` decreases the zoom level, but `Ctrl++` does not increase it again. I also could not find a setting in the app to increase or reset the zoom afterwards. After that, the desktop app keeps opening with the smaller zoom level that was previously set.

### Operating system
Windows 10 Pro (build 19042)

### Application version
Element Desktop 1.12.15

### How did you install the app?
Per-user Windows installation in %LOCALAPPDATA%\\element-desktop using Squirrel (Update.exe), with Element.exe version 1.12.15 signed by Element.

### Homeserver
Not relevant

### Will you send logs?
No