Mail composer: Move to CC freezes the app

[benbucksch]

Reproduction

• Write email or reply, with multiple people in To
• Do not have the CC line open
• Click on one of the persons
• Click [CC] to move him/her to CC.

Actual result

• App freezes
• Error: (null).openPopup()

Expected result

• CC line opens
• Person is removed from To line
• Person is added to CC line
• When sending, person is in CC:, not To: list

[benbucksch]

TypeError: Cannot read properties of undefined (reading 'openPopup')
  at instance$36 (../../../../app/frontend/Shared/PersonAutocomplete/PersonEntry.svelte:41:23)
  at new PersonEntry (../../../../app/frontend/Shared/PersonAutocomplete/PersonEntry.svelte:4:25)
  at create_each_block$A (../../../../app/frontend/Shared/PersonAutocomplete/PersonEntry.svelte:4:25)
  at create_fragment$36 (../../../../app/frontend/Shared/PersonAutocomplete/PersonsAutocomplete.svelte:2:9)
  at addPerson_handler_1 (../../../../app/frontend/Shared/PersonAutocomplete/PersonsAutocomplete.svelte:17:58)
...
(11 additional frame(s) were not displayed)

[benbucksch]

I don't know why the <PersonsAutocomplete> does not properly observe changes in mail.cc.

I've disabled the button for now, to avoid this bug, in git commit 093ed2d. See this commit for hints at roughly where in the code the problem is.