Fixed possible issue with sending invalid message to the delegate or delegate not receiving a message at all

The problem here was that previously the app checked whether delegate responded to a selector
```
if ([delegate respondsToSelector:@selector(authManagerDidAuthenticate:)]) {
```

But then, a line below, a completely different selector is called:
```
[delegate authManagerDidAuthenticate:self credentials:coordinator.credentials authInfo:info];
```

This can result in the auth callback message not being sent at all, or being sent to an object that does not handle such message (and thus resulting in a crash). This simple change fixes the issue.