Trying to start a voice call via iPhone telephone list creates a strange invite event

A friend of mine tried to start a voice call via the iPhone telephone list. This resulted in a strange event being created in our direct 2-person chat room:
```json
{
"content": {
"membership": "invite"
},
"event_id": "$:matrix.org",
"origin_server_ts": 1565296334710,
"sender": "@:matrix.org",
"state_key": "@fs_:matrix.org",
"type": "m.room.member",
"unsigned": {
"age": 31441188
},
"room_id": "!:matrix.org"
}
```
Now the room title indicated that there are three persons in the room although the membership list only displays two.

Reproduce the issue by starting a voice call from the iPhone telephone list in a direct two-person chat and inspect the resulting room events. Done means no unexpected m.room.member invite event is created and the room title continues to show the correct two-person membership.

Written by the indexing model from the issue text.