FlashPrint crashes when VPN is on

FlashPrint 5.2.0 crashes when opening the `Connect Machine` dialogue.

It didn't crash when `--unshare=network` is passed (though you can't connect to any machines obviously), or when the VPN is disabled.

`ifconfig` output for that VPN:
```
tun0: flags=4305 mtu 1360
inet 10.39.192.186 netmask 255.255.240.0 destination 10.39.192.186
inet6 fd10:39:192:1::10b9 prefixlen 64 scopeid 0x0
unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 txqueuelen 500 (UNSPEC)
RX packets 2034 bytes 397629 (388.3 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 3041 bytes 184571 (180.2 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
```

The `valgrind` output is useless:
```
==33== Invalid read of size 2
==33== at 0x7B2B80: ??? (in /app/extra/share/FlashPrint5/FlashPrint)
==33== by 0x4C7D07: ??? (in /app/extra/share/FlashPrint5/FlashPrint)
==33== by 0x596F2E7: QThreadPrivate::start(void*) (qthread_unix.cpp:342)
==33== by 0x5F3C5E1: start_thread (pthread_create.c:479)
==33== by 0x61BD472: clone (clone.S:95)
==33== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==33==
==33==
==33== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==33== Access not within mapped region at address 0x0
==33== at 0x7B2B80: ??? (in /app/extra/share/FlashPrint5/FlashPrint)
==33== by 0x4C7D07: ??? (in /app/extra/share/FlashPrint5/FlashPrint)
==33== by 0x596F2E7: QThreadPrivate::start(void*) (qthread_unix.cpp:342)
==33== by 0x5F3C5E1: start_thread (pthread_create.c:479)
==33== by 0x61BD472: clone (clone.S:95)
==33== If you believe this happened as a result of a stack
==33== overflow in your program's main thread (unlikely but
==33== possible), you can try to increase the size of the
==33== main thread stack using the --main-stacksize= flag.
==33== The main thread stack size used in this run was 8388608.
```