assertion triggered after upgrading to ejabberd 17.x

[darix]

The subscription attribute can be optional if no subscription exists according to processone/ejabberd#1590 .

it seems the assert should be changed to a normal if then?

https://github.com/cdidier/irssi-xmpp/blob/master/src/core/rosters.c#L276

[cdidier]

The first "if (..." should be changed to "if (subscription == NULL || .." to set the subscription to NONE.

[darix]

while we are at it could we also fix 15:43:51 -!- Irssi: critical Source ID 1 was not found when attempting to remove it

[cdidier]

Fixed with 2c55602.