AntimicroX crashes at startup when the environment variable `DISPLAY` is unset

### Is there an existing issue for this?

- [x] I searched the existing issues and did not find anything similar.

### Current Behavior

AntimicroX crashes at startup with a segmentation fault when the environment variable `DISPLAY` is unset under scroll (sway fork).

### Expected Behavior

It doesn't crash.

### Steps To Reproduce

Run `DISPLAY= antimicrox` from the terminal.

### Environment

```markdown
Program Version 3.6.1
Compiled from packaging: 3.6.1
Built Against SDL 2.32.68
Running With SDL 2.32.70
Using Qt 6.11.1
Using Event Handler: uinput
Compositor type: wayland
Host OS: arch Version: unknown Architecture: x86_64
```

### Anything else?

Terminal output of `DISPLAY= antimicrox --log-level debug`:

```Selecting uinput as a default event generator.[09:42:43.204] ⚪VERBOSE AntiMicroX version: 3.6.1 Package: 3.6.1 Type: Release (file /src/common.cpp:205)
[09:42:43.204] ⚪VERBOSE SDL version: 2.32.70 (Compiled with: 2.32.68) (file /src/common.cpp:215)
[09:42:43.204] ⚪VERBOSE Host OS: arch Version: unknown Architecture: x86_64 (file /src/common.cpp:217)
[09:42:43.204] ⚪VERBOSE Platform name: wayland (file /src/common.cpp:219)
[09:42:43.204] 🐞DEBUG Socket's state: QLocalSocket::UnconnectedState
[09:42:43.204] 🐞DEBUG Server name: ""
[09:42:43.204] 🐞DEBUG Socket descriptor: -1
[09:42:43.204] 🐞DEBUG The connection hasn't been established:
error text -> QLocalSocket::ConnectionRefusedError
error text 2 -> "QLocalSocket::connectToServer: Connection refused"
[09:42:43.204] 🐞DEBUG Socket is not valid
[09:42:43.204] 🐞DEBUG Socket's state: QLocalSocket::UnconnectedState
[09:42:43.204] 🐞DEBUG Server name: ""
[09:42:43.204] 🐞DEBUG Socket descriptor: -1
[09:42:43.204] 🐞DEBUG "/home/maxigaz/.local/share/antimicrox/icons"
[09:42:43.204] 🐞DEBUG "/usr/local/share/antimicrox/icons"
[09:42:43.204] 🐞DEBUG "/usr/share/antimicrox/icons"
[09:42:43.204] 🐞DEBUG "/home/maxigaz/.local/share/icons"
[09:42:43.204] 🐞DEBUG "/usr/local/share/icons"
[09:42:43.204] 🐞DEBUG "/usr/share/icons"
[09:42:43.204] 🐞DEBUG Theme name: "Papirus-Dark"
[09:42:43.205] ⚪VERBOSE EventHandlerFactory: requested handler=uinput (file /src/eventhandlerfactory.cpp:51)
[09:42:43.205] ⚪VERBOSE EventHandlerFactory: initializing uinput handler. (file /src/eventhandlerfactory.cpp:56)
[09:42:43.205] 🐞DEBUG Displays don't have local data: create new instance of X11Extras
[09:42:43.205] ❌ERROR Received: SIGSEGV (segmentation fault) (file /src/main.cpp:86)
[09:42:43.205] ❗WARN Stack trace: (file /src/main.cpp:99)
[09:42:43.205] ❗WARN antimicrox(+0xb05fa) [0x5631b27895fa] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN /usr/lib/libc.so.6(+0x3e6f0) [0x7fdb1623e6f0] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN /usr/lib/libX11.so.6(XkbKeycodeToKeysym+0x4) [0x7fdb17d588f4] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN antimicrox(+0x241bbe) [0x5631b291abbe] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN antimicrox(+0x2451b0) [0x5631b291e1b0] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN antimicrox(+0xbc13a) [0x5631b279513a] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN antimicrox(+0x708ce) [0x5631b27498ce] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN /usr/lib/libc.so.6(+0x27781) [0x7fdb16227781] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN /usr/lib/libc.so.6(__libc_start_main+0x89) [0x7fdb162278b9] (file /src/main.cpp:102)
[09:42:43.205] ❗WARN antimicrox(+0x841b5) [0x5631b275d1b5] (file /src/main.cpp:102)
[09:42:43.205] ⚪VERBOSE Closing logger (file /src/logger.cpp:62)
[1] 48360 segmentation fault (core dumped) DISPLAY= antimicrox --log-level debug
```