Fix error reporting during mail setup

[CarlSchwan]

Previously only the generic (and not useful) error message was
displayed when a more useful message was available and could have
been displayed instead.

The error message is located in error.data.message and not error.message

[welcome]

Thanks for opening your first pull request in this repository! ✌️

[ChristophWurst]

Thanks a lot.

I guess this then (at least partially) solves #3006.

[ChristophWurst]

Now i remember that the message isn't always set. Did you try this with debug mode on or off? I think message is omitted in production mode.

[CarlSchwan]

Now i remember that the message isn't always set. Did you try this with debug mode on or off? I think message is omitted in production mode.

I just tested with "debug" => false in my config.php and this particular message is still displayed.

[GretaD]

On master, when you add wrong data you always get: Unexpected error during account creation

On this branch:
When i add the host but wrong pasword: Creating account failed:Connection to IMAP at mx.nextcloud.com:993 failed. Authentication failed.

when i "forget" to add the host: Creating account failed:Connection to IMAP at :993 failed. Error connecting to mail server.

So this is a great improvement already :)

[GretaD]

You need to squash and sign your pr and its good to go

[CarlSchwan]

On master, when you add wrong data you always get: Unexpected error during account creation

On this branch:
When i add the host but wrong pasword: Creating account failed:Connection to IMAP at mx.nextcloud.com:993 failed. Authentication failed.

when i "forget" to add the host: Creating account failed:Connection to IMAP at :993 failed. Error connecting to mail server.

So this is a great improvement already :)

Thanks :)

Some wording could probably be improved but that's probably material for another MR :)

I squashed both commit and signed the MR.