wingpanel crashes by toggling airplane mode

## Prerequisites
- [x] I have searched open and closed issues for duplicates.

## Describe the bug
So I have an issue with connecting to network after returning from suspend, I think it might be [this issue](https://github.com/elementary/wingpanel-indicator-network/issues/18), not sure yet. The wireless looks disabled on some deeper level than just `network-manager` so I tried flipping my airplane mode switch (Fn+F3 on my Acer Cloudbook 11). The network usually starts working but the wingpanel crashes *every time*.

### To Reproduce
Steps to reproduce the behavior:
1. Switch airplane mode ON / OFF (single toggle is enough for me but I usually do both ON & OFF to resolve the network issue)
2. Crash:
- there is a notification with airplane icon stuck on the screen, closing it makes it reappear again;
- wingpanel consumes 100 % of one CPU core, but is responsive (I can interact with indicators, open App launcher etc.);
- also all text input fields are disabled (I cannot type in terminal, search in App launcher, nor in the Monitor app) - this last symptom seems to go away after some alt-tabbing, but it can be unrelated or the crash finished in the meantime.

### Expected behavior

Not a crash :)

### Logs
I have saved several coredumps:
[wingpanel-crash-coredump.txt](https://github.com/elementary/wingpanel/files/3694222/wingpanel-crash-coredump.txt)
[wingpanel-crash-coredump2.txt](https://github.com/elementary/wingpanel/files/3694223/wingpanel-crash-coredump2.txt)

The second one is from today.

## Platform Information


- [ ] I'm using the latest version from git that I've manually compiled
- [x] I'm using the latest released stable version

## Additional context