Attempting to add locations to a clock with a customized display format will cause a crash

Note: I'm in the EST time zone if it matters.

Steps to reproduce:
(for best results, this should be the only clock applet on your panel, occasionally having more than one clock somewhere on your system may get different behavior)

1. Add a clock to a panel
2. Right click on it, go to preferences
3. Set it to 12 hour format
4. Go to the location tab, add "London (Heathrow Airport), East and South East England, United Kingdom"
5. Click OK, you will get "Clock" has quit unexpectedly and all clocks will be removed from all panels.

Note that changing "show seconds" while also adding a location will also cause this problem.

Workaround procedure:

It seems like you can only add a location if you are using all default display settings (i.e., not showing seconds, and only using 24 hour time format), though I did not test every single setting. It doesn't seem to matter whether this location is in your time zone or not, even adding locations in my time zone also crashes it.

So basically you have to add all the locations you think you might need, *then* customize your time format.

1. Add a clock to a panel
2. Right click on it, go to preferences
3. Go to the location tab, add "London (Heathrow Airport), East and South East England, United Kingdom" (and any other locations you need)
4. Make any display customizations you want (12 hour clock, show seconds, etc

Note that adding another location at this point will crash it, but it seems like changing everything back to defaults on the General tab will let you add another location.

This bug is new in Ubuntu 20.04; I didn't have this issue in 18.04.