Invitation: Move respondToInvitation() from EMail to Calendar/

[benbucksch]

This is about the refactoring from the last commit on PR #461, now git commit abc66c7 on branch neil/refac.
This ticket is about fixing this branch.

One known bug is:

Env

• neil@beonex account
• EWS

Reproduction

1. Start Mustang, go to Email
2. Click on email "Owl ActiveSync 128 from 115" or any of the other emails with an open (not responded) invitation
3. Click on [Accept]

Actual result

After step 2 (view only):

• You see an invitation
• You see error "Must have event to find calendar"
• You see the error message twice
• 
• No error on console (!)

After step 3:

• selectedCalendar is undefined

error.ts:6 TypeError: Cannot read properties of undefined (reading 'respondToInvitation')
    at respond (Invitation.svelte:59:28)
    at onAccept (Invitation.svelte:62:11)
    at HTMLButtonElement.myOnClick (Button.svelte:79:13)

• This is on line: await selectedCalendar.respondToInvitation(message, response); . That means selectedCalendar is undefined.

Expected result

• All errors are on the local error console, and are also logged to server
• No error during display
• No error during [Accept]
• Response is processed.

Originally posted by @benbucksch in #461 (comment)

[benbucksch]

The entire code to load calendars in Invitation.svelte is iffy.

[benbucksch]

The new .calendar property on the MailAccount subclasses is also not good, but that would be easier to fix with #155 , which I plan to work on, so it's easier to leave it as-is and fix it later.

[NeilRashbrook]

The error message is displayed on the page because of the block:

    {:catch ex}
      {ex?.message}
      {ex}
    {/await}

message.loadEvent() is supposed to, well, load the event, so I'm not sure offhand why the event is missing at this point.

As for the selected calendar, it's not getting set because of the previous error.

[NeilRashbrook]

I've pushed commit a32cd92 to branch neil/refac just to see what effect it has for you.

[benbucksch]

Is there a particular reason why you load the calendars after loading the message event?